Tobacco

The incidence of lung cancer in both men and women increased dramatically in the last 25 years worldwide, but is now falling in many developed countries. The association of smoking with lung cancer is indisputable and causative mechanisms have been identified: cigarette tobacco is responsible for one-third of all deaths from cancer in the UK. Smoking not only causes lung cancer, it is also associated with cancer of the mouth, larynx, oesophagus and bladder. Smoking is discussed on page 806.

Alcohol

Alcohol is associated with cancers of the upper respiratory and gastrointestinal tracts, and it also interacts with tobacco in the aetiology of these tumours. It may be associated with an increased risk of breast cancer.

Diet

Dietary factors have been attributed to account for one-third of cancer deaths, although it is often difficult to differentiate these from other epidemiological factors. For example, the incidence of stomach cancer is particularly high in the Far East, while breast and colon cancers are more common in the Western, economically more developed countries. Many associations have been observed without a causative mechanism being identified between the incidence of cancer and the consumption of dietary fibre, red meat, saturated fats, salted fish, vitamin E, vitamin A and many others. Food and its role in the causation of gastrointestinal cancer is discussed in Chapter 5 (see p. 218). Increasing levels of obesity in the developed world have been associated with increases in women of cancers associated with oestrogenic stimulation of the breast and endometrium.

Environmental/occupational

Ultraviolet light is known to increase the risk of skin cancer (basal cell, squamous cell and melanoma). The incidence of melanoma is therefore particularly high in the white Anglo-Celtic population of Australia, New Zealand and South Africa, where exposure to UV light is combined with a genetically predisposed population.

Arsenical contamination of water supplies has been linked to high incidence of lung and colon cancers in Southeast Asia particularly where bore holes are the main water source.

Occupational factors. In 1775, Percival Pott described the association between carcinogenic hydrocarbons in soot and the development of scrotal epitheliomas in chimney sweeps. The principal causes now are asbestos (lung and mesothelial cancer) and polycyclic hydrocarbons from fossil fuel combustion (skin, lung, bladder cancers). Organic chemicals, such as benzene, may cause the development of bone marrow conditions such as myelodysplastic syndrome or acute myeloid leukaemia.

Infectious agents

The geographical distribution of a rare malignancy suggests that it might be caused by, or associated with, an infective agent. Chronic persistent infection provides growth stimulation while many viruses contain transforming viral oncogenes.

T-cell leukaemia, seen almost exclusively in residents of the southern island of Japan and in the West Indies, is caused by infection with the locally endemic retrovirus HTLV-1 (human T-cell leukaemia virus) and integration of the oncogene, TAX, into the cellular genome.

Hepatocellular carcinoma occurs in patients with hepatitis B and C virus infections and Burkitt’s lymphoma and nasopharyngeal carcinoma are associated with the Epstein–Barr virus. EBV is also linked with Hodgkin’s lymphoma (see p. 459).

Patients with HIV infection or immunosuppression from organ transplantation have an increased incidence of EBV-related lymphoma and herpesvirus-8-associated Kaposi’s sarcoma.

The incidence of cervical cancer had increased among younger women in association with sexually transmitted HPV (human papillomavirus) infection types 16 and 18, for which an effective vaccine is now available.

Bacterial infection with Helicobacter pylori predisposes to the development of gastric cancer and gastric lymphoma, while Schistosoma japonicum infection predisposes to the development of squamous cell carcinomas in the bladder.

Medications

Oestrogens have been implicated in the development of vaginal, endometrial and breast carcinoma. Certain cytotoxic drugs given, e.g. for Hodgkin’s lymphoma (see later) are themselves associated with an increased incidence of secondary acute myelogenous leukaemia (AML), bladder and lung cancer. Androgens have been associated with both benign and malignant liver tumours.

Radiation

Accidental. The nuclear disasters of Hiroshima, Nagasaki and Chernobyl led to an increased incidence of leukaemia after 5–10 years in the exposed population as well as increased incidences of thyroid and breast cancer. Radiation workers are at an increased risk of malignancy due to occupational exposure unless precautions are taken to minimize this using personal and environmental shielding and to record and limit the amount of personal exposure.

Therapeutic. Long-term survivors following radiotherapy, e.g. for Hodgkin’s lymphoma, have an increased incidence of cancer, particularly at the radiation field margins.

Diagnostic. Imaging procedures involving radiation exposure are associated with an increased risk of cancer. This risk is cumulative, dose dependent and time dependent, i.e. children are at higher risk than adults. The cancer risk of various common investigations is shown in Table 9.5. All doctors should strive to minimize diagnostic exposure to radiation where possible using alternative modalities such as ultrasound or MRI. Good documentation of radiation doses is required. This is particularly so in children and pregnant women.

Table 9.5 Radiation exposure from common diagnostic radiological procedures

UK background radiation is 2.6 mSv per year. 1 mSv carries a lifetime cancer risk of 1 in 17 500 and 5 mSv a risk of 1 in 3500.

Modified from: Smith-Bindman R, Lipson J, Marcus R et al. Archives of Internal Medicine 2009; 169:2078–2086 and Fazel R, Krumholz HM, Wang Y et al. New England Journal of Medicine 2009; 361:849–857.

Epidemiology

The incidence and mortality from cancer varies by tumour type and geographical region across the world.

Geographical distribution

The incidence of cancer across the world is dependent on the local environmental factors, the diet and the genetics of the population (see above) (Figs 9.3, 9.4). Age is also a factor as most cancers occur in those over the age of 65 who comprise 3.3% of the population in Africa compared with 15.2% in Europe. Reproductive patterns also influence breast cancer. Migrating individuals often take on the risks of the local environmental factors.

Figure 9.3 The most common causes of death from cancer worldwide, excluding non-melanoma skin cancers (NMSC) 2002 estimates.

(From: http://info.canceresearchuk.org/cancerstats/world/the-global-picture/)

Figure 9.4 Percentage of all deaths due to cancer in the different regions of the world.

(From: http://info.canceresearchuk.org/cancerstats/world/the-global-picture/)

Serum tumour markers

Tumour markers are intracellular proteins or cell surface glycoproteins released into the circulation and detected by immunoassays. Examples are given in Table 9.7. Values in the normal range do not necessarily equate with the absence of disease and a positive result must be corroborated by histology as these markers can be seen in many benign conditions. They are most useful in the serial monitoring of response to treatment. As discussed in subsequent sections, a proportion of low-grade B-cell lymphomas and a majority of cases of myeloma will produce a monoclonal paraprotein of intact immunoglobulin molecule or light chains. This acts as a valuable tumour marker in the diagnosis and assessment of response.

Table 9.7 Serum tumour markers

Cancer imaging

Radiological investigation by experts is required at various stages: at initial diagnosis and staging of the disease, during the monitoring of treatment efficacy, at the detection of recurrence and for the diagnosis and treatment of complications.

The choice of investigations needs to be guided by the patient’s symptoms and signs, site and histology of the cancer, the curative or palliative potential of treatment and the utility of the information in guiding treatment. The investigations are described under each tumour type.

Contrast agents are used for increased structural discrimination and can be further enhanced with functional specificity for metabolically active tissue with 19fluorodeoxy-glucose uptake and CT-positron emission tomography (CT-PET scan) as used extensively in head and neck cancer, lung cancer and lymphoma. Radionuclide imaging of sentinel lymph nodes is used to guide lymphatic surgery in breast cancer and melanoma. Tumour targeted contrast agents can improve detection rates such as the radiolabelled MAb rituximab for lymphoma or radiolabelled small molecules such as octreotide for neuroendocrine tumours. Research into the use of reporter agents which become visible only upon activation within the tumour environment holds the promise of greater sensitivity and specificity in the future.

Biopsy and histological examination

The diagnosis of cancer may be suspected by both patient and doctor but advice about treatment can usually only be given on the basis of a tissue diagnosis. This may be obtained by endoscopic, radiologically-guided or surgical biopsy or on the basis of cytology (e.g. lung cancer diagnosed by sputum cytology). Malignant lesions can be distinguished morphologically from benign ones by the pleiomorphic nature of the cells, increased numbers of mitoses, nuclear abnormalities of size, chromatin pattern and nucleolar organization and evidence of invasion into surrounding tissues, lymphatics or vessels. The degree of differentiation (or conversely of anaplasia) of the tumour has prognostic significance: generally speaking, more differentiated tumours have a better prognosis than poorly-differentiated ones. In some tumours where the surgical procedure will vary depending on the presence of malignancy, an intraoperative histological opinion can be rapidly obtained using a tissue sample processed using ‘frozen section’ techniques, which requires the availability of a histopathologist. This obviates the need for the sample to be paraffin embedded, which takes hours to days.

Tissue tumour markers. Immunocytochemistry, using monoclonal antibodies against tumour antigens, is very helpful in differentiating between lymphoid and epithelial tumours and between some subsets of these, for example T- and B-cell lymphomas, germ cell tumours, prostatic tumours, neuroendocrine tumours, melanomas and sarcomas. However, there is much overlap in the expression of many of the markers and some adenocarcinomas and squamous carcinomas do not bear any distinctive immunohistochemical markers that are diagnostic of their primary site of origin.

Molecular markers of genetic abnormalities have long been available in the haematological cancers and are increasingly available in solid cancers. For example, fluorescent in situ hybridization (FISH, see p. 40) can be used to look for characteristic chromosomal translocations, e.g. in lymphoma and leukaemia, as well as deletions or amplifications, e.g. in breast cancer (see genetic basis of cancer, p. 45). Tissue microarrays can identify patterns of multiple genomic alterations and single nucleotide polymorphisms (SNPs), e.g. in breast cancer and lymphoma (see p. 35), and RNA assays with RT-PCR can be used to identify tissue of origin with prognostic and predictive relevance.

Genomics and proteomics are being investigated in order to target new (and expensive) therapies, e.g. imatinib in CML and GIST, trastuzumab and lapatinib in breast cancer and erlotinib in lung cancer.

Adjuvant therapy for solid tumours

This is defined as treatment given, in the absence of macroscopic evidence of metastases, to patients at risk of recurrence from micrometastases, following treatment given for the primary lesion. ‘Neoadjuvant’ therapy, alternatively, is given before primary surgery, to both shrink the tumour to improve the local excision and treat any micrometastases as soon as possible.

Micrometastatic spread by lymphatic or haematological dissemination often occurs early in the development of the primary tumour and can be demonstrated by molecular biological methods capable of detecting the small numbers (1 in 10⁶) of circulating cells. Studies correlating prognosis with histological features of the primary cancer, e.g. differentiation, invasion of blood vessels or regional lymph nodes and molecular markers, e.g. Her2 in breast cancer, enable risk stratification and increasing individualization of therapy.

The success of adjuvant treatment across many tumour types relies upon careful selection of patients according to defined risk criteria and the reduction of treatment toxicity to reach a balanced risk/benefit ratio. Relative risk reductions in the order of 12–33% and absolute improvements in 5–10-year survival of 5–25% (dependent upon the pre-existing risk) have been achieved in common epithelial cancers such as lung, bowel, breast and prostate, with greater absolute improvements in the more sensitive germ cell tumours.

While these improvements currently translate into many lives saved from common diseases at a public health level, the majority who receive such treatment do not benefit because they were already cured, or because the cancer is resistant to the treatment. Better tests, e.g. gene arrays and circulating tumour cells, are being developed to identify those with the micrometastases who really need treatment. On an individual patient basis the decision on whether adjuvant treatment will be worthwhile must include consideration of other factors such as the patient’s life expectancy, concurrent medical conditions and lifestyle priorities.

Staging

Before a decision about treatment can be made, not only the type of tumour but also its extent and distribution need to be established. Various ‘staging investigations’ are therefore performed before a treatment decision is made. To be useful clinically the staging system must subdivide the patients into groups of different prognosis which can guide treatment selection.

The staging systems vary according to the type of tumour and may be site specific (see Hodgkin’s lymphoma, p. 461), or the TNM (tumour, node, metastases) classification shown in Table 15.29, which can be adapted for application to most common cancers.

Performance status

In addition to anatomical staging, the person’s age and general state of health need to be taken into account when planning treatment. The latter has been called ‘performance status’ and is of great prognostic significance for all tumour types (Table 9.8). Performance status reflects the effects of the cancer on the patient’s functional capacity. An alternative performance rating scale is by Karnowsky. With a performance status of 2, response to and survival following treatment are greatly reduced for most tumour types.

Table 9.8 Eastern Cooperative Oncology Group (ECOG) performance status scale

DNA damaging drugs

Alkylating agents act by covalently binding alkyl groups and their major effect is to cross-link DNA strands, interfering with DNA synthesis and causing strand breaks. Despite being among the earliest cytotoxic drugs developed, they maintain a central position in the treatment of cancer. Melphalan is one of the original nitrogen mustards and is used in multiple myeloma. Chlorambucil is used in Hodgkin’s lymphoma and chronic lymphocytic leukaemia. Other common alkylating agents include cyclophosphamide and ifosfamide, as well as the nitrosoureas, carmustine (BCNU), bendamustine, lomustine (CCNU) and busulfan used in chronic myeloid leukaemia. Tetrazines also alkylate DNA; dacarbazine is used in Hodgkin’s lymphoma and temozolomide in malignant gliomas.

Table 9.9 Chemotherapy: some cytotoxic drugs

Platinum compounds. Cisplatin, carboplatin and oxaliplatin cause interstrand cross-links of DNA and are often regarded as non-classical alkylating agents. They have transformed the treatment of testicular cancer (cisplatin) and have a major role against many other tumours, including lung, ovarian and head and neck (cis or carboplatin) and gastrointestinal (oxaliplatin) cancer. Toxicity, as for other heavy metals, includes renal and peripheral nerve damage.

Antimetabolites

Antimetabolites are usually structural analogues of naturally occurring metabolites that interfere with normal synthesis of nucleic acids by falsely substituting purines and pyrimidines in metabolic pathways. Antimetabolites can be divided into:

Folic acid antagonists, e.g. methotrexate. This is structurally very similar to folic acid and binds preferentially to dihydrofolate reductase, the enzyme responsible for the conversion of folic acid to folinic acid. It is used widely in the treatment of solid tumours and haematological malignancies. Folinic acid is often given to ‘rescue’ normal tissues from the effects of high doses of methotrexate.

Pyrimidine antagonists. 5-Fluorouracil (5FU) consists of a uracil molecule with a substituted fluorine atom. It acts by blocking the enzyme thymidylate synthase, which is essential for pyrimidine synthesis. 5-Fluorouracil has a major role in the treatment of solid tumours, particularly gastrointestinal cancers. Oral capecitabine is metabolized to 5FU and tegafur with uracil and calcium folinate are used in gastrointestinal and breast cancers.

Arabinosides inhibit DNA synthesis by inhibiting DNA polymerase. Cytosine arabinoside (cytarabine, Ara-C) is used almost exclusively in the treatment of acute myeloid leukaemia where it remains the backbone of therapy, while its analogue gemcitabine is proving useful in a number of solid cancers such as lung, breast, pancreas and ovary. Fludarabine is used in the treatment of B cell chronic lymphocytic leukaemia; it is also used in reduced intensity stem cell transplantation (see this chapter) because of its immunosuppressive effect. Other related drugs have found niche applications in acute leukaemia (cladribine, clofarabine, nelarabine/AraG) and myelodysplasia (azacytidine).

Purine antagonists, e.g. 6-mercaptopurine and 6-tioguanine, which are both used almost exclusively in the treatment of acute leukaemia.

DNA repair inhibitors

Epipodophyllotoxins. These are semisynthetic derivatives of podophyllotoxin which inhibit topoisomerase. Topoisomerase enzymes allow unwinding and uncoiling of supercoiled DNA. Etoposide is a drug used in a wide range of cancers and works by maintaining DNA strand breaks by inhibiting the enzyme topoisomerase II. Topoisomerase I inhibitors such as irinotecan and topotecan have also proved active against lung, colon, ovary and cervix cancer.

Cytotoxic antibiotics. The anthracyclines act by intercalating adjoining nucleotide pairs on the same strand of DNA and by inhibiting topoisomerase II DNA repair. They have a wide spectrum of activity in haematological and solid tumours. Doxorubicin and its congener epirubicin are two of the most widely used of all cytotoxic drugs but have cumulative toxicity to the myocardium. Pegylated liposomal doxorubicin is used for Kaposi’s sarcoma and as second-line treatment for advanced ovarian cancer with reduction of cardiotoxicity, but increased toxicity to the skin on the palms of the hands and soles of the feet. Amsacrine is a similar drug used occasionally in acute myeloid leukaemia. Bleomycin and mitomycin are also intercalating agents which promote the cleavage of DNA and RNA. Bleomycin has a particular toxicity to the lung causing interstitial fibrosis.

Antitubulin agents

Vinca alkaloids. Drugs such as vincristine, vinblastine and vinorelbine act by binding to tubulin and inhibiting microtubule formation during mitosis (see p. 20). They are used in the treatment of haematological (vincristine and vinblastine) and non-haematological cancers (vinorelbine). They are associated with neurotoxicity due to their anti-microtubule effect and must never be given intrathecally as this is lethal.

Taxanes. Paclitaxel and docetaxel bind to tubulin dimers and prevent their assembly into microtubules. They are active drugs against many cancers such as ovarian, breast and lung cancer. Taxanes can cause neurotoxicity and hypersensitivity reactions and patients should be premedicated with steroids, H1 and H2 histamine antagonists prior to treatment.

Other toxicities

Cardiotoxicity. This is a rare side-effect of chemotherapy, usually associated with anthracyclines such as doxorubicin, and can present as an acute arrhythmia during administration or cardiac failure due to cardiomyopathy after chronic exposure. This effect is dose-related and can largely be prevented by restricting the cumulative total dose of anthracyclines within the safe range (equivalent to 450 mg/m² body surface area cumulative doxorubicin dose). The risk of anthracycline cardiomyopathy is also dependent on other treatments such as trastuzumab or radiotherapy as well as other cardiac risk factors such as hypertension, smoking and hypercholesterolaemia. Cardiotoxicity can also be reduced by using the analogue epirubicin or by reducing peak drug concentrations through delayed release preparations such as liposomal doxorubicin. 5-Fluorouracil and its prodrug capecitabine can cause cardiac ischaemia.

Anthracycline dilated cardiomyopathy with congestive heart failure.

Neurotoxicity. This occurs predominantly with the vinca alkaloids, taxanes and platinum analogues (but not carboplatin). It is dose-related and cumulative. Chemotherapy is usually stopped before the development of a significant polyneuropathy, which once established is only partially reversible. Vinca alkaloids such as vincristine must never be given intrathecally as the neurological damage is progressive and fatal.

Nephrotoxicity. Cisplatin (but not oxaliplatin or carboplatin), methotrexate and ifosfamide can potentially cause renal damage. This can usually be prevented by maintaining an adequate diuresis during treatment to reduce drug concentration in the renal tubules and careful monitoring of renal function.

Sterility and premature menopause. Some anticancer drugs, particularly alkylating agents, but also anthracyclines and docetaxel, may cause gonadal damage resulting in sterility and in women the loss of ovarian oestrogen production, which may be irreversible.

In males, the storage of sperm prior to chemotherapy should be offered to the patient when chemotherapy is given with curative intent.

In females, collection of oocytes to be fertilized in vitro and cryopreserved as embryos for subsequent implantation is most successful; however it is also possible to collect and freeze by vitrification of unstimulated oocytes. Cryopreservation of ovarian tissue and retrieval of viable oocytes for subsequent fertilization is still experimental. The recovery of gonadal function is dependent upon the status before treatment and in women this is mostly related to age since menarche, with those under the age of 40 having significantly more ovarian reserve.

Secondary malignancies. Anticancer drugs have mutagenic potential and the development of secondary malignancies, predominantly acute leukaemia, is an uncommon but particularly unwelcome long-term side-effect in patients otherwise cured of their primary malignancies. The alkylating agents, anthracyclines and epipodophyllotoxins are particularly implicated in this complication.

Autologous stem cell transplantation

Most anticancer drugs have a sigmoid dose–response relationship which suggests that, up to a point, a higher dose of a cytotoxic drug will induce a greater response. However, increasing cytotoxic drug dose is often not possible, owing to toxicity. For those chemotherapeutic agents with a dose-limiting toxicity of bone marrow failure, infusion of previously harvested haemopoietic stem cells is able to ‘rescue’ the haemopoietic system and permits the use of higher doses to overcome tumour drug resistance. Haemopoietic stem cells are either collected from the patient’s bone marrow, or more commonly by leucopheresis from the peripheral blood following stem cell mobilization from the marrow niche by the administration of the growth factor granulocyte colony-stimulating factor (G-CSF) with or without chemotherapy. These stem cells are stored by cryopreservation and then reinfused intravenously after an intensive, chemotherapy regimen. This approach has been particularly effective in relapsed leukaemias, lymphomas, myeloma and germ cell tumours. However, tumour contamination of the reinfused stem cells remains a reality. Treatment-related mortality is in the region of 1–5%. Such an approach is also being evaluated for the treatment of severe autoimmune disease, such as Crohn’s.

Allogeneic stem cell transplantation

Interferons

Interferons are naturally occurring cytokines that mediate the cellular immune response. They are both antiproliferative and stimulate humoral and cell-mediated immune responses to the tumour that can result in an antitumour effect if the host effector mechanisms are fully competent.

Alpha-interferon (IFN-α) has been used to treat advanced melanoma and renal cell carcinoma.

Treatment with IFN has side-effects (see p. 321), most commonly flu-like symptoms, which tend to diminish with time, and fatigue, which generally does not, and can be treatment limiting. IFN was given as a daily subcutaneous injection, but conjugation with polyethylene glycol (PEG interferon) has led to a reduction in frequency of injection and severity of side-effects.

Interleukins

Interleukin 2, a recombinant protein, is used to activate T-cell responses, often in conjunction with interferon-stimulated B-cell activation. Antitumour activity has been observed in renal cell carcinoma and melanoma with responses in 10–20% of patients, occasionally for prolonged periods. Toxicity is common; acutely this includes the capillary leak syndrome with hypotension and pulmonary oedema, while autoimmune thyroiditis and vitiligo occur later.

Immunotherapy

While the most dramatic evidence for immunotherapy is seen in the allogeneic HSCT above, activation of the immune system using Bacille Calmette–Guérin (BCG) for bladder cancer induces responses in 60% of patients. Certain antigens that are specific to cancer cells, such as sequences of tumour immunoglobulin from B-cell lymphomas, or melanoma antigens, have been used as tumour vaccines together with manipulation of the immune system to overcome tolerance.

Immunomodulatory drugs (IMIDs) thalidomide, lenalidomide

This family of immunomodulatory drugs are being increasingly used in a range of malignancies, such as myeloma, chronic lymphocytic leukaemia (CLL) and myelodsyplastic syndrome (MDS) as well some solid tumours. They have anti-angiogenic functions as well as affecting cytokine production, tumour/stromal interactions and T-cell co-stimulatory functions. They are all considered teratogenic and should be avoided in women of reproductive potential unless extra precaution is taken against conceiving.

Proteasome inhibitors

The proteasome degrades redundant or damaged proteins that have been labelled by a process called ubiquitination. Such proteins include cyclins and cyclin-dependent kinases as well as factors in the NFκB pathway. Inhibition of the proteasome leads to apoptosis in cancer cells and is synergistic with other treatments such as steroids and chemotherapy. Bortezomib is the first of such inhibitors to reach clinical practice and is used in myeloma as well as some types of NHL.

Monoclonal antibodies

Monoclonal antibodies (MAb) directed against tumour cell surface antigens are ‘humanized’ by being genetically engineered and have a range of functions:

Side-effects are those of hypersensitivity to the foreign protein and specific cross-reactivities, e.g. trastuzumab for the myocardium, bevacizumab for the mucosa and renal tubule and cetuximab for the skin follicles.

Intracellular signal inhibitors (Table 9.12)

Many cancer cells are transformed by the activity of the protein products of oncogenes that signal growth by phosphorylation of tyrosine residues on the intracellular portion of growth factor receptors. Small molecule inhibitors have many pharmacokinetic advantages over the MAb inhibitors. The first example was the tyrosine kinase inhibitor (TKi) imatinib, which specifically inhibits the BCR-ABL fusion oncoprotein and c-Kit. This compound is an extremely effective treatment for chronic myeloid leukaemia and gastrointestinal stromal tumours (GIST), which are characterized by the presence of the c-Kit target. Lapatinib, which inhibits Her2, has increased survival in breast cancer. The less specific TKIs sunitinib and sorafenib which inhibit signalling by EGFR and VEGFR have proved effective in metastatic renal cancer, while erlotinib and gefitinib have shown activity in lung cancer. Vemurafenib is a kinase inhibitor and has a specificity for BRAF-V600 as used in malignant melanoma ( p. 1226). Many other similar molecules are in preclinical or early clinical development but heterogeneity within a single tumour occurs and genomic anomalies may not all be represented in a single biopsy specimen.

Table 9.12 Targeted therapies in cancer*

Gene therapy

Antisense oligonucleotides are short sequences of DNA bases which specifically inhibit complementary sequences of either DNA or RNA. As a result, they can be generated against genetic sequences, which are specific for tumour cells. Their clinical development has been hampered by poor uptake by tumour cells and rapid degradation by natural endonucleases. However, one antisense sequence directed against the Bcl-2 oncogene has been shown to have an antitumour effect in patients with non-Hodgkin’s lymphoma. Viral vectors for the transfection of tumour cells in vivo are being tested as a way of delivering specific replacement gene therapy in head and neck cancers.

Genetic abnormalities in leukaemia

Leukaemic cells often have a somatically acquired cytogenetic abnormality, which may be of prognostic, as well as diagnostic, significance.

These genetic alterations change the normal cell regulating process by interfering with the control of normal proliferation, blocking differentiation, maintaining an unlimited capacity for self-renewal and, lastly, promoting resistance to death signals, i.e. decreased apoptosis.

The first non-random chromosomal abnormality to be described was the Philadelphia (Ph) chromosome, which is associated with CML in 97% of cases (see Fig. 9.16a). The Ph chromosome is also found in ALL, the incidence in the latter illness increasing with age. The translocation is shown schematically in Figure 9.16a. The Ph chromosome is an abnormal chromosome 22, resulting from a reciprocal translocation between part of the long arm of chromosome 22 and chromosome 9. The resulting karyotype is described as t(9; 22)(q34; q11). The molecular consequences of the translocation are that part of the Abelson proto-oncogene (c-ABL) normally present on chromosome 9 is translocated to chromosome 22, where it comes into juxtaposition with a region of chromosome 22 named the ‘breakpoint cluster region’ (BCR). The new ‘fusion’ gene BCR-ABL is capable of being expressed as a chimeric messenger RNA, which has been identified in cells from patients with CML. When translated, this produces a fusion protein that has tyrosine kinase activity and enhanced phosphorylating activity compared with the normal protein, resulting in altered cell growth, stromal attachment and apoptosis. The breakpoint differs in CML and Ph-positive ALL, leading to the production of two different tyrosine kinase proteins with molecular weights of 210 kDa and 190 kDa, respectively. It is unclear whether the presence of BCR-ABL is sufficient for the development of the disease. It has been shown that normal subjects can carry low levels of the BCR-ABL fusion gene in their blood without developing leukaemia. Other genetic and cytogenetic abnormalities are often seen in leukaemic cells (Table 9.17).

Table 9.17 WHO classification of acute leukaemia

a The entities included in this group are defined almost identically to the corresponding entity in the French–American–British (FAB) classification.

Modified from: Jaffe ES, Harris NL, Stein H et al. (eds) World Health Organization Classification of Tumours. Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissues. Lyon: IARC Press; 2008, with permission from the World Health Organization.

As well as cytogenetic and molecular aberrations, epigenetic modification via abnormal methylation patterns and chromatin modification due to histone acetylation is increasingly understood to be involved in oncogenesis and may represent potential therapeutic targets.

Acute myeloid leukaemia (AML)

In AML, the prognosis is dependent on a range of key variables, the two main ones being age and cytogenetics (Fig. 9.14; Table 9.19).

Figure 9.14 Prognosis related to cytogenetics and molecular data in AML Outcome of younger adults with AML treated in the MRC AML10 and AML12 trials stratified according to cytogenetic and molecular abnormalities.

(Reproduced with permission from Smith ML, Hills RK, Grimwade D. Independent prognostic variables in acute myeloid leukaemia. Blood Reviews 2011; 25(1):39–51.)

Table 9.19 AML risk factors

Treatment with curative intent is undertaken in the majority of adults below the age of 60 years, provided there is no significant co-morbidity. Treatment success reflects the cytogenetic pattern. Those at ‘low risk’ are treated with moderately intensive combination chemotherapy. This always includes an anthracycline such as daunorubicin and cytosine arabinoside (cytarabine) and consolidation with a minimum of four cycles of treatment given at 3–4-week intervals. Patients with low-risk disease do not benefit from allogeneic stem cell transplantation during their first complete remission because the risks outweigh benefits. Those at ‘intermediate risk’ are a heterogeneous group. When possible, they should be given consolidation chemotherapy after an initial remission has been achieved followed by allogeneic transplantation only in those who are deemed at increased risk of relapse because of other risk factors, e.g. mutational data. Patients with high-risk disease should proceed to a stem cell transplant in CR1 because they respond poorly to conventional chemotherapy and have a high risk of relapse.

Complete remission (CR) will be achieved in about 80% of patients under the age of 60. Failure is due to either resistant leukaemia (10%) or death due to infection or bleeding (10%). Approximately 50% of those entering complete remission will be cured (i.e. approximately 40% overall) although this varies from 60–70% in the favourable cytogenetic group to 10–20% in the adverse cytogenetic group.

The initial treatment of the older patient is much more contentious. Older patients tolerate cytotoxic therapy less well than younger patients due to co-morbidities and their disease is often more aggressive in its biology, e.g. adverse cytogenetics are more common with increasing age. Reduced intensity allogeneic transplantation is increasingly being used for this group but is limited by the toxicity of this treatment.

The management of recurrence is undertaken on an individual basis, since the overall prognosis is very poor despite the fact that second remissions may be achieved. Long survival following recurrence is rarely achieved without allogeneic transplantation. Experimental therapy should be considered. The use of minimal residual disease monitoring may allow the detection of a subgroup of patients during initial therapy who require treatment intensification, e.g. allograft, as well as patients in CR who are at the early stages of relapse and need preemptive therapy before frank marrow relapse occurs.

Newer agents that target the FLT3 mutation, present in a significant proportion of cases of AML, are in clinical trials in conjunction with conventional chemotherapy. Other novel therapies that are being considered in AML include chemotherapy labelled monoclonal antibodies (gemtuzumab ozogamicin) and hypomethylating agents (azacytidine).

Acute promyelocytic leukaemia (APML)

This is a variant of AML, occurring in 10–15% of cases, that is characterized by the translocation t(15; 17) and with particular morphological features. There is an almost invariable coagulopathy, which was a major cause of early death. The empirical discovery that all-trans-retinoic acid (ATRA) causes differentiation of promyelocytes and rapid reversal of the bleeding tendency was a major breakthrough. APML is treated with ATRA combined with several courses of chemotherapy. Complete remission and molecular remission occur in at least 90% of younger adults with APML and at least 70% will expect to be cured. Transplantation may be necessary either if the leukaemia is not eliminated at the molecular level, or following recurrence and reinduction therapy. Arsenic trioxide, which induces apoptosis via activation of the caspase cascade (see p. 33), is used with resistant or relapsed disease and is under investigation as first-line therapy.

Acute lymphoblastic leukaemia (ALL)

This condition may present in leukaemic phase with significant marrow involvement (ALL) or may present as localized disease, typically a mediastinal mass (lymphoblastic lymphoma). The tumour cells in each condition are indistinguishable and similar therapies are therefore used. The overall strategy for the treatment of ALL differs in detail from that for AML. Remission induction is undertaken with combination chemotherapy including vincristine, a glucocorticoid, an anthracycline and asparaginase. Once remission is achieved, the details of consolidation will be determined by the anticipated risk of failure. Intensive consolidation of remission with variable numbers of chemotherapy cycles comprising cytotoxics with different mechanisms of action has been standard practice, including the administration of high-dose methotrexate. In those patients with high-risk features (see below) or an HLA-matched sibling donor, allogeneic transplantation is recommended upon achieving first complete remission (CR1).

A major difference between therapy for ALL and AML is the need for central nervous system directed therapy. Prophylaxis should be given with intrathecal chemotherapy under platelet cover if necessary, as soon as blasts are cleared from the blood. Depending upon risk this may be continued for up to 2 years and complemented by high doses of systemic cytosine arabinoside (cytarabine) or methotrexate. Cranial irradiation was previously given to all patients to reduce the risk of relapse within the central nervous system; some risk adapted strategies reserve this only for those patients at very high risk.

Additionally, after intensive induction and consolidation, maintenance therapy for 2 years is required to reduce the risk of disease recurrence. This typically comprises 2 years of treatment with methotrexate and mercaptopurine, although more intensive regimens are used by many groups.

Prognosis

The prognosis (Fig. 9.15) of ALL in childhood is now excellent: complete remission is achieved in almost all, with up to 80% being alive without recurrence at 5 years. Failure occurs most frequently in those with high presentation blast counts or a t(9;22) translocation. Current treatment strategies are to lessen therapy for ‘good risk’ children in order to avoid some of the long-term consequences of therapy such as avascular necrosis of bone, infertility, neurotoxicity and cardiotoxicity.

Figure 9.15 Overall survival in 2628 children of different ages with newly diagnosed ALL participating in consecutive studies conducted at St Jude Children’s Research Hospital from 1962 to 2005.

(From Pui C-M, Robinson LL, Lock T. Acute lymphoblastic leukaemia. Lancet 2008; 371:1030–1043, Figure 3, with permission.)

The situation is far less satisfactory for adults, the prognosis getting worse with advancing years. Co-morbidity and t(9; 22) translocation increases in frequency with age. Overall, the complete remission rate is 70–80%. Disease that is refractory to first-line therapy carries a very poor prognosis. Between 30% and 40% of patients continue in durable first remissions, resulting in approximately 25–30% overall patient cure. Increasing numbers of patients are being transplanted for this condition, including those with sibling donors and those high-risk patients with an available unrelated donor. Imatinib used in conjunction with chemotherapy increases the response rate and quality of response in patients with the t(9;22) translocation and ALL. As with AML, most recurrences occur within the first 3 years and the outcome is extremely poor. Second remissions, though usually achieved, are rarely durable except following allogeneic transplantation. Isolated extramedullary recurrences, however, may be cured.

FURTHER READING

Diller L. Adult primary care after childhood acute lymphoblastic leukemia. N Engl J Med 2011; 365:1417–1424.

Pui CH, Robison LL, Look AT. Acute lymphoblastic leukaemia. Lancet 2008; 371:1030–1043.

Chronic myeloid leukaemia (CML)

Chronic myeloid leukaemia (CML), which accounts for about 14% of all leukaemias, is one of the family of myeloproliferative neoplasms (MPNs) and is almost exclusively a disease of adults with the peak of presentation being between 40 and 60 years. It is defined by the presence of the Philadelphia chromosome (Fig. 9.16), either demonstrated cytogenetically (95%) or molecularly (5%). Unlike the acute leukaemias which are either rapidly reversed or rapidly fatal, CML has a more slowly progressive course, which if not initially cured, will be followed eventually by ‘blast crisis’ transformation to acute leukaemia (75% myeloid, 25% lymphoid) or myelofibrosis with death in a median of 3–4 years.

Figure 9.16 The Philadelphia chromosome (Ph). (a) The long arm (q) of chromosome 22 has been shortened by the reciprocal translocation with chromosome 9. (b) The Philadelphia chromosome is formed by a reciprocal translocation of part of the long arm (q) of chromosome 22 to chromosome 9. It is seen in 90–95% of patients with chronic myeloid leukaemia. The karyotype is expressed as 46XX, (9;22)(q34;q11).

Investigations

Blood film showing blast cells in CML.

Blood count. Hb low (normochromic and normocytic) or normal, WBC raised (usually >100 × 10⁹/L), platelets low, normal or raised.

Blood film. Neutrophilia with the whole spectrum of mature myeloid precursors. Elevated basophils and eosinophils. Increased numbers of blasts are suggestive of accelerated phase or blast crisis.

Bone marrow aspirate. Increased cellularity, increased myeloid precursors. Cytogenetics reveals t(9; 22) translocation (the Philadelphia chromosome) (Fig. 9.16b).

Fluorescence in situ hybridization (FISH) or reverse transcriptase polymerase chain reaction (RT-PCR) are used to demonstrate the cytogenetic/molecular abnormality. These are also used to quantitatively monitor response to therapy.

Chronic lymphocytic leukaemia (CLL)

This is the most common leukaemia, occurring predominantly in later life and increasing in frequency with advancing years (median age of presentation between 65 and 67 years). It results from the clonal expansion of small lymphocytes and is almost invariably (95%) B cell in origin. The majority of patients are asymptomatic, identified as a chance finding on a blood count performed for another indication. Other patients, however, present with the features of marrow failure or immunosuppression. The median survival is about 10 years and prognosis correlates with clinical stage at presentation (Table 9.21). A number of cytogenetic and molecular abnormalities are now recognized as being of prognostic significance (see below). This condition may present in leukaemic phase with significant marrow involvement (CLL) or may present as localized disease (small lymphocytic lymphoma, SLL). The tumour cells in each condition are indistinguishable and a similar therapeutic approach is therefore used. A pre-malignant condition, monoclonal B cell lymphocytosis (MBL) exists where there are less than the 5 × 10⁹/L B-cells required for a diagnosis of CLL. Some of these have CLL phenotype and may progress to CLL.

Table 9.21 The Rai and Binet staging systems for chronic lymphocytic leukaemia^a

Prognostic biomarkers

The clinical course of CLL is variable. Several markers are used to supplement clinical stage and have been shown to predict progression and survival. Variations in predictor cut-off levels have limited their widespread application.

Cytogenetic abnormalities are detected in >90% of cases. Patients with an isolated deletion of 13q have an excellent prognosis, in contrast to those with either 11q deletion or 17p deletion (the sites of the tumour suppressor genes ATM and TP53, respectively) who tend to have a rapidly evolving clinical course. In those tumours that demonstrate a high level of mutation within the variable region of the rearranged immunoglobulin heavy chain (IgVH), the clinical course is more indolent than those where the IgVH sequence more closely resembles that of the germline. Expression of ZAP70, a 70 kDa tyrosine kinase protein, correlates well with mutational status. Patients with <20% expression of ZAP70 have median 10-year survival of >50%; in >20% expression the median survival was <5 years. High expression of CD38 on leukaemic cells may also indicate adverse prognosis.

Fluorescence in situ hybridization photomicrograph of a patient with CLL. (a) 17p (green probe) and 11q (red probe) shows two green signals (TP53 deletion) with normal diploid complement of 11q. (b) 12 centromere (green probe) and 13q14 (red probe) shows three green signals (trisomy 12) with normal diploid complement of 13q.

(Courtesy of Debra Lillington, Barts and the London NHS Trust.)

Hairy cell leukaemia (HCL)

HCL is a clonal proliferation of abnormal B (or very rarely T) cells which, as in CLL, accumulate in the bone marrow and spleen. It is a rare disease, median age at presentation is 52 years old and the male to female ratio is 4 : 1. The bizarrename relates to the appearance of the cells on a blood film and in the bone marrow – they have an irregular outline owing to the presence of filament-like cytoplasmic projections.