MOLECULAR BIOLOGY OF HUMAN CANCERS.

MOLECULAR BIOLOGY OF HUMAN CANCERS. What is commonly called ‘human cancer’ comprises in fact more than 200 different diseases. Together, they account for about one fifth of all deaths in the industrialized countries of the Western World. Likewise, one person out of three will be treated for a severe cancer in their life-time. In a typical Western industrialized country like Germany with its 82 million inhabitants, 400,000 persons are newly diagnosed with cancer each year, and |200,000 succumb to the disease. Since the incidence of most cancers increases with age, these figures are going to rise, if life expectancy continues to increase. If one considers the incidence and mortality by organ site, while ignoring further biological and clinical differences, cancers fall into three large groups (Figure 1.1). Cancers arising from epithelia are called ‘carcinomas’. These are the most prevalent cancers overall. Four carcinomas are particular important with regard to incidence as well as mortality. Cancers of the lung and the large intestine (colon and rectum, o13) are the most significant problem in both genders, together with breast cancer (o18) in women and prostate cancer (o19) in men. A second group of cancers are not quite as prevalent as these ‘major four’ cancers. They comprise carcinomas of the bladder (o14), stomach (o17), liver (o16), kidney (o15), pancreas, esophagus, and of the cervix and ovary in women. Each accounts for a few percent of the total cancer incidence and mortality. Each of them is roughly as frequent as all leukemias or lymphomas (o10) taken together. The most prevalent cancers are those of the skin (o12), not shown in figure 1.1. They are rarely lethal, with the important exception of melanoma. Cancers of soft tissues, brain, testes, bone, and other organs are relatively rare; but can constitute a significant health problem in specific age groups and geographic regions. For instance, testicular cancer is generally the most frequent neoplasia affecting young adult males, with an incidence of 1% in this group in some Scandinavian countries and in Switzerland. The health situation in less-industrialized countries differs principally from that in the highly industrialized part of the world because of the continuing, recurring or newly emerged threat of infectious diseases, which include malaria, tuberculosis, and AIDS. Nevertheless, cancer is important in these countries as well, with different patterns of incidence and often higher mortalities. Cancers of the stomach (o17), liver (o16), bladder (o14), esophagus, and the cervix are each endemic in certain parts of the world (Figure 1.2). Often, they manifest at younger ages than in industrialized countries. Conversely, of the major four cancers in industrialized countries, only lung cancer has the same impact in developing countries. 2 CHAPTER 1 This snapshot view of present-day cancer incidence of course conceals changes over time (Figure 1.3). For instance, large-scale industrialization and the spread of cigarette smoking are generally associated with an increased incidence of lung, kidney, and bladder cancer. On the positive side, improvements in general hygiene and food quality may have contributed to the spectacular decrease in stomach cancer Figure 1.1 Incidence (top) and mortality (bottom) of cancers (cases per year) by organ site for females (grey bars) and males (black bars) in Germany in 2000. Data are from the Robert Koch Institute (). AN INTRODUCTION TO HUMAN CANCERS 3 incidence that is continuing in industrialized countries (o17.1). On the negative side, prostate and testicular cancer appear to have increased over the last decades. In prostate cancer, a slight increase in the age-adjusted incidence is exacerbated by the overall aging of the population (o19.1).In some regions, the incidence of melanoma has escalated in an alarming fashion. This increase is not related to the aging of the population, but perhaps to life-style factors (o12.1). One important aim of molecular biology research on human cancers is to understand the causes underlying the geographical and temporal differences in cancer incidence. This understanding is one important prerequisite for cancer prevention (o20). Obviously, the prospects for prevention are brightest for those cancers that exhibit large geographical differences or the great changes over time in their incidences. To give just one example: The incidence of prostate cancer of East Asia residents may be 10-20-fold lower than that of their relatives who grow up in the USA (o19.1). It is easy imagining the potential for prevention, if the causes for this difference were understood. Unfortunately, overall, neither incidence nor mortality of human cancer have been much diminished by conscious human intervention over the last decades. The mainstay of treatment of the ‘big four’ cancers and of the carcinomas in the second group outlined above remain surgery, radiotherapy, and chemotherapy, as they were 30 years ago. Surgery and radiotherapy are often successful in organ-confined cases, and chemotherapy is moderately efficacious for some advanced cancers. In general, only modest improvements have been made in cure and survival rates for these. Importantly, the quality of life for the patients is now widely accepted as a criterion Figure 1.2 Mortality of selected cancers by organ site in different regions of the World In each group of bars from left to right: World average, Africa, North-America, SouthAmerica, North-West Europe, China. Data source: Shibaya et al, BMC Cancer 2, 37ff 4 CHAPTER 1 for successful therapy. Modern cancer therapy recognizes that not every malignant tumor can be cured by the means presently available. So, treatment needs to be carefully chosen to maximize the chance for a cure while retaining a maximum of life quality. Providing a better basis for this choice will perhaps constitute the most immediate application of new insights on the molecular biology of cancers (o21). In addition, palliative treatments have become more sophisticated and pain medications are less restrictively administered. Nevertheless, the treatment of metastatic carcinomas remains the weakest point of current cancer therapy and a crucial goal of cancer research (o22). Figure 1.3 Trends in the mortality of selected cancers in the USA The original data figure is from the American Cancer Society. Great steps towards successful treatment have been made with specific cancers, unfortunately mostly from the third group above. These improvement have had little effect on the impact of cancer on the overall population, but have helped many individuals, often young people and children. Formerly incurable leukemias and lymphomas can now be successfully treated by chemotherapy and/or stem cell transplantation, particularly in children and young adults. Likewise, the rise in testicular cancer incidence is stemmed by highly efficacious chemo- and radiotherapy, with cure rates exceeding 90%. Obviously, there is a need to understand why these cancers, but not others respond so well to the chemotherapeutic drugs currently available. It is hoped that a better understanding of the molecular and cellular basis underlying this difference will eventually open the door to successful treatment of the major carcinomas, as will the development of novel drugs and novel therapies based on the results of molecular biological cancer research (o22). AN INTRODUCTION TO HUMAN CANCERS 5 1.2 CAUSES OF CANCER Since the genetic constitution of mankind hardly changes within a century and differs only moderately between human populations in different parts of the world, the changes in the incidences of individual cancers over time and their geographical variation to a large extent reflect environmental effects. Cancers are caused by exogenous chemical, physical, or biological carcinogens. They act on humans who, however, vary in their ability to cope with them due to differences in their genetic constitution (o2.3, o3.4) and – not to forget - their psychological, social, and economic conditions. Endogenous processes in the human body also contribute to the development of cancer, on their own or by interacting with exogenous agents. The mechanisms of carcinogenesis in humans are often multifactorial and complex. Different factors may act by different mechanisms and at different stages of tumor development. In experimental animals carcinogens can be applied in a controlled fashion and the individual steps and interactions can therefore be analyzed more precisely. It is, e.g., possible in some cases to distinguish between initiating and promoting agents as well as complete carcinogens, or between carcinogens and co-carcinogens. In these laboratory models, initiating carcinogens are usually mutagens, while promoting agents act by facilitating the expansion of cells with altered DNA. These distinctions are more difficult to apply in real human cancers. For instance, tobacco smoke is a human carcinogen, without a shade of doubt. In fact, it contains a variety of different carcinogens, some of which may act as initiators and some as promoters, and some as both. Nicotine itself is almost certainly not a direct carcinogen, but a potent alkaloid which acts not only on the central nervous system, but also influences cell signaling and cell interactions in the airways and in the lung. So, it would have to be classified as a co-carcinogen. Similarly complex interactions take place during skin carcinogenesis caused by UV radiation (o12.1). Moreover, the actions of carcinogens and co-carcinogens are modulated by genetic differences in the human population, which is outbred, unlike many laboratory animals. As a consequence, it is often difficult in humans to elucidate exactly by which mechanism a potential carcinogen acts, even though it is clearly identified as being associated with a specific cancer by epidemiological data. Attempts at prevention must therefore often be started before the relationship between a carcinogen and cancer development is fully understood (o20). Nevertheless, precise elucidation of the mechanisms is helpful and insights from molecular biology are beginning to contribute to improved prevention of cancer (o20). Many carcinogens have been established as important in human cancer, in one or the other way. Exogenous carcinogens can be classified into chemical, physical, and biological agents. Table 1.1 provides an overview of these classes, with prominent examples for each class. For some carcinogens the evidence is very strong, while for others the notion ‘carcinogen’ has to be applied in a broader sense. Another type of classification issued by the World Health Organization groups human carcinogens 6 CHAPTER 1 by the level of available evidence. The most important criteria of this classification are listed in Table 1.2. Chemical carcinogens come from different sources and comprise very different chemicals (Figure 1.4). Inorganic compounds like nickel, cadmium, or arsenic are encountered in the workplace or are present as contaminants in water. Organic compounds acting as carcinogens can be aliphatic, like nitrosamines, which occur in smoked and pickled foods, or trichloro-ethylene, which is used for cleaning. Nitrosamines are thought to contribute to stomach cancer, in particular (o17.1) Aromatic compounds like benzopyrenes and arylamines are generated from natural sources by burning, and are among the many carcinogens in tobacco smoke. They also present a danger in the workplace, e.g. during coal processing and dye production and use, respectively. Arylamines are thought to cause bladder cancer, in particular (o14.1). Polyaromates like benzopyrene are also released into the environment by burning of coal and fuels. Natural compounds produced by plants and molds can be highly carcinogenic. Aflatoxin B1 is implicated as a carcinogen in liver cancer (o16.1) and is the most infamous of many chemically diverse compounds in this group. Medical drugs can be carcinogenic, notably those used in cytostatic tumor therapy like cyclophosphamide, nitrogen mustards, and platinum compounds. Various hormones and hormone-like compounds from natural and pharmaceutic sources also influence the development of cancers in specific tissues, e.g. in the breast (o18.1) and prostate (o19.1). Doubtless, the most abundant exogenous carcinogen is oxygen. The form present in air, dioxygen, is relative inert and, of course, safe when fully reduced towards H2O. However, partially reduced oxygen or dioxygen activated towards its singlet state are highly reactive and can be mutagenic (Box 1.1). Reactive oxygen species are formed at low levels during normal metabolism and are produced at increased rates during certain physiological processes such as immune defense and inflammation. Their concentrations can also be increased during the metabolism of some exogenous compounds, e.g. quinones (o20.2), and by pathophysiological states such as iron overload (o16.1). Table 1.1. Types and examples of human carcinogens Type of carcinogen Examples Chemical carcinogens Nickel, cadmium, arsenic, nitrosamines, trichloroethylene, arylamines, benzopyrene, aflatoxins, reactive oxygen species Physical carcinogens UV irradiation (specifically UVB), ionizing radiation Biological carcinogens Human papilloma virus (e.g. strain 16), Epstein-BarrVirus, Hepatitis virus B, Helicobacter pylori, Schistosoma mansoni Endogenous processes DNA replication, metabolic reactions generating reactive oxygen species, chronic inflammation AN INTRODUCTION TO HUMAN CANCERS 7 Table 1.2. Classification of human carcinogens according to the WHO/IARC Group Definition Group 1 The agent is carcinogenic in humans. The exposure circumstance entails exposures that are carcinogenic to humans. Group 2A The agent is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans. Group 2B The agent is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans. Group 3 The agent (or exposure circumstance) is not classifiable as to carcinogenicity in humans. Group 4 The agent (or exposure circumstance) is probably not carcinogenic to humans. NB: the group definitions apply to single agents or mixtures. Physical carcinogens: Any energy-rich radiation can in principle act as a carcinogen, depending on dose and absorption. Visible light is not usually carcinogenic, unless it is absorbed by ‘photosensitizing agents’ which generate reactive oxygen species. UVB irradiation is an important carcinogen in the skin (o12.1), and its effect is augmented by UVA. In contrast, UVC is strongly absorbed in the non-cellular protective layers of the skin and does not usually act as a carcinogen. J-Radiation from natural, industrial, and iatrogenic sources (e.g., used in X-ray diagnostics) can penetrate into and through the body. It is carcinogenic to the extent to which it is absorbed, damaging DNA and cells by direct absorption but also indirectly by generating reactive oxygen species. Damage and carcinogenicity by J-radiation therefore depend on the concentration of oxygen and also on the repair capacity (o3.3). Radioactive E-radiation and specifically D-radiation is most dangerous when nuclides are incorporated, e.g. of cesium, uranium, and plutonium. The effect of radioactive isotopes depends also on their distribution in the body. For instance, radioactive iodine is accumulated in the thyroid gland and therefore causes specifically thyroid cancers, whereas radioactive cesium isotopes tend to become enriched in the urinary bladder. The potential carcinogenicity of microwave and radio wavelength electromagnetic radiation are, of course, the subject of public debate. Biological carcinogens: Certain viruses and bacteria act as biological carcinogens in man. Specific strains of human papilloma viruses (HPV16 and HPV18) are established as causative factors in cervical and other genital cancers (oBox 5.1). They also influence the development of cancers of the skin and of the head and neck, and perhaps others as well. Papovaviruses like SV40 (simian virus 40) cause cancers in animals and partially transform human cells in vitro (o5.3), but 8 CHAPTER 1 whether they actually cause human cancers is a controversial issue. The best evidence exists for mesothelioma, a rare cancer which may be caused by the combined action of SV40 and asbestos. Specific herpes viruses can also act as carcinogens or co-carcinogens, e.g. human herpes virus 8 (HHV8) in Kaposi sarcoma (o Box 8.1) or Epstein-Barr virus (EBV) in lymphomas (o10.3). The hepatitis B virus (HBV) with its DNA genome is certainly involved in the causation of liver cancer, although in a complex fashion (o16.3), as is the hepatitis C virus (HCV) which has an RNA genome. Human retroviruses such as HIV facilitate the development of cancers mostly by interfering with the immune system, but HTLV1 (human T-cell leukemia virus) causes a rare leukemia by direct growth stimulation of T-cells (oBox 4.1). Figure 1.4 Some chemical carcinogens NNK is 4-(Methyl-nitrosamino)-1-(3-pyridyl)-1-butanone, a nitrosamine like dimethylnitrosamine in the upper right corner. AN INTRODUCTION TO HUMAN CANCERS 9 While there are many speculations on a carcinogenic role of bacteria, definitive evidence exists for a relationship between Helicobacter pylori infection and stomach cancer (o17.3). More generally, bacterial infections may contribute to inflammation which can promote cancer development. Schistosoma trematodes also cause cancer in humans, mostly in the urinary bladder (o14.1). Endogenous carcinogens: How effective exogenous carcinogens elicit cancer in a specific person depends strongly on an individual’s exposure, specific responses, and general health. So, endogenous processes are in any case involved in cancer development through modulation of the response to exogenous carcinogens. However, cancers may also be caused by strictly endogenous processes: ¾Normal metabolism generates carcinogenic compounds such as nitrosamines, aromatic amines, quinones, reactive aldehydes, and – as mentioned above – reactive oxygen species. The concentration of these potential carcinogens may vary depending on factors like diet or physical activity, but a minimum level is associated with any level of metabolic activity and any type of diet. Potent protective and detoxification mechanisms exist for many of these compounds, but they can never be perfect. ¾In the same vein, damage to cells and specifically DNA occurs at a minimum rate spontaneously and particular during cell proliferation, e.g. by errors in replication or by spontaneous chemical reactions of DNA bases (o3.1). The potentially huge number of such errors is kept at bay by very efficient DNA repair mechanisms specifically directed at typical errors of this kind. In addition, damaged cells are removed by apoptosis and other mechanisms. These protective mechanisms, however, cannot be perfect, either. An Introduction to Human Cancers..................................................................... 1 1.1 An overview of the cancer problem .................................................................. 1 1.2 Causes of cancer............................................................................................... 5 Box 1.1 Reactive oxygen species ........................................................................ 10 1.3 Characteristic Properties of Cancers and Cancer Cells................................ 11 Box 1.2: Hallmarks of Cancer ............................................................................. 18 1.4 Characterization and Classification of Cancers in the Clinic ....................... 17 1.5 Treatment of Cancer....................................................................................... 21 Further reading..................................................................................................... 23 2 Tumor Genetics .................................................................................................... 25 2.1 Cancer as a genetic disease............................................................................ 26 2.2. Genetic alterations in cancer cells ................................................................ 27 2.3 Inherited predisposition to cancer.................................................................. 37 2.4 Cancer genes .................................................................................................. 42 2.5 Accumulation of genetic and epigenetic changes in human cancers ............. 44 Further reading..................................................................................................... 45 Box 2.1 Tumor viruses in human cancers ........................................................... 46 3 DNA Damage and DNA Repair .......................................................................... 47 3.1 DNA damage during replication: base excision and nucleotide excision repair.............................................................................................................. 48 3.2 Nucleotide excision repair and crosslink repair ............................................ 55 3.3 Strand-break repair ........................................................................................ 62 3.4 Defects in DNA repair and cancer susceptibility ........................................... 66 3.5 Cell protection mechanisms in cancer............................................................ 68 Further reading..................................................................................................... 70 4 Oncogenes.............................................................................................................. 71 4.1 Retroviral oncogenes...................................................................................... 72 4.2 Slow-acting transforming retroviruses........................................................... 75 4.3 Approaches to the identification of human oncogenes................................... 78 4.4 Functions of human oncogenes ...................................................................... 84 Further reading..................................................................................................... 89 Box 4.1 Carcinogenesis by HTLV-I.................................................................... 90 5 Tumor Suppressor Genes .................................................................................... 91 5.1 Tumor suppressor genes in hereditary cancers.............................................. 92 5.2 RB1 and the cell cycle..................................................................................... 97 5.3 TP53 as a different kind of tumor suppressor .............................................. 101 vii PART I – MOLECULES, MECHANISMS, AND CELLS 5.4 Classification of tumor suppressor genes..................................................... 109 Further reading................................................................................................... 111 Box 5.1 Human papilloma viruses..................................................................... 112 6 Cancer Pathways ................................................................................................ 113 6.1 Cancer Pathways.......................................................................................... 114 6.2 MAPK signaling as a cancer pathway ......................................................... 115 6.3 The PI3K pathway ........................................................................................ 119 6.4 Regulation of the cell cycle by the MAPK and PI3K pathways ................... 123 6.5 Modulators of the MAPK and PI3K pathways ............................................. 126 6.6 The TP53 network......................................................................................... 129 6.7 Signaling by TGFE factors .......................................................................... 131 6.8 Signaling through STAT factors ................................................................... 132 6.9 The NFNB pathway....................................................................................... 135 6.10 Developmental regulatory systems as cancer pathways ............................ 137 Further reading................................................................................................... 144 7 Apoptosis and Replicative Senescence in Cancer............................................ 145 7.1 Limits to cell proliferation............................................................................ 146 7.2 Mechanisms of apoptosis.............................................................................. 150 7.3 Mechanisms of diminished apoptosis in cancer ........................................... 156 7.4 Replicative senescence and its disturbances in human cancers................... 159 Further reading................................................................................................... 164 Box 7.1: Human aging and cancer..................................................................... 165 8 Cancer Epigenetics ............................................................................................. 167 8.1 Mechanisms of epigenetic inheritance ......................................................... 168 8.2 Imprinting and X-inactivation ...................................................................... 170 8.3 DNA methylation .......................................................................................... 174 8.4 Chromatin structure...................................................................................... 179 8.5 Epigenetics of cell differentiation................................................................. 182 8.6 Epigenetics of tissue homeostasis................................................................. 185 Further reading................................................................................................... 191 Box 8.1 Carcinogenesis by HIV 192 9 Invasion and metastasis ..................................................................................... 193 9.1 Invasion and metastasis as multistep processes........................................... 194 9.2 Genes and proteins involved in cell-to-cell and cell-matrix adhesion......... 197 9.3 Genes and proteins involved in extracellular matrix remodeling during tumor invasion................................................................................. 202 9.4 Angiogenesis ................................................................................................. 206 9.5 Interactions of invasive tumors with the immune system ............................. 210 9.6 The importance of tumor-stroma interactions.............................................. 212 Further reading................................................................................................... 216 Box 9.1 Tumor hypoxia and its consequences .................................................. 217 viii PART II - HUMAN CANCERS 10 Leukemias and Lymphomas............................................................................ 219 10.1 Common properties of hematological cancers........................................... 221 10.2 Genetic aberrations in leukemias and lymphomas..................................... 223 10.3 Molecular biology of Burkitt lymphoma..................................................... 226 10.4 Molecular biology of CML ......................................................................... 232 10.5 Molecular biology of PML ......................................................................... 237 Further reading................................................................................................... 242 11 Wilms Tumor (nephroblastoma) .................................................................... 243 11.1 Histology, etiology and clinical behavior of Wilms tumors ....................... 244 11.2 Genetics of Wilms tumors and the WT1 gene............................................. 246 11.3 Epigenetics of Wilms tumors and the ‘WT2’ locus..................................... 250 11.4 Towards an improved classification of Wilms tumors ............................... 252 Further reading................................................................................................... 253 12 Cancers of the skin ........................................................................................... 255 12.1 Carcinogenesis in the skin.......................................................................... 256 12.2 Squamous cell carcinoma........................................................................... 260 12.3 Basal Cell Carcinoma................................................................................. 262 12.4 Melanoma ................................................................................................... 266 12.5 Tumor antigens ........................................................................................... 269 Further reading................................................................................................... 270 13 Colon Cancer .................................................................................................... 271 13. 1 Natural history of colorectal cancer ......................................................... 272 13.2 Familial Adenomatous Polyposis Coli and the WNT pathway .................. 273 13.3 Progression of Colon Cancer and the Multi-Step Model of Tumorigenesis .......................................................................................... 280 13.4 Hereditary nonpolyposis colon carcinoma ................................................ 282 13.5 Genomic instability in colon carcinoma..................................................... 284 13.6 Inflammation and colon cancer.................................................................. 285 Further reading................................................................................................... 287 Box 13.1 Positional cloning of tumor suppressor genes in hereditary cancers. 288 14 Bladder Cancer................................................................................................. 289 14.1 Histology and etiology of bladder cancer .................................................. 290 14.2 Molecular alterations in invasive bladder cancers.................................... 297 14.3 Molecular alterations in papillary bladder cancers .................................. 302 14.4 A comparison of bladder cancer subtypes.................................................. 304 Further reading................................................................................................... 305 Box 14.1: Tumor suppressor candidates at 9q in bladder cancer ...................... 306 15 Renal Cell Carcinoma ...................................................................................... 307 15.1 The diversity of renal cancers .................................................................... 308 15.2 Cytogenetics of renal cell carcinomas........................................................ 310 ix 15.3 Molecular biology of inherited kidney cancers .......................................... 311 15.4 Von-Hippel-Lindau syndrome and renal carcinoma.................................. 316 15.5 Molecular biology of clear cell renal carcinoma....................................... 321 15.6 Chemotherapy and immunotherapy of renal carcinomas .......................... 324 Further reading................................................................................................... 326 16 Liver Cancer ..................................................................................................... 327 16.1 Etiology of liver cancer .............................................................................. 328 16.2 Genetic changes in hepatocellular carcinoma ........................................... 331 16.3 Viruses in HCC........................................................................................... 336 Further reading................................................................................................... 339 Box 16.1 Hepatocellular carcinoma in experimental animals........................... 340 17 Stomach Cancer................................................................................................ 341 17.1 Etiology of stomach cancer ........................................................................ 342 17.2 Molecular mechanisms in gastric cancer................................................... 345 17.3 Helicobacter pylori and stomach cancer.................................................... 348 Further reading................................................................................................... 354 Box 17.1: Barrett esophagus and esophageal cancer......................................... 355 18 Breast Cancer.................................................................................................... 357 18.1 Breast biology............................................................................................. 358 18.2 Etiology of breast cancer............................................................................ 364 18.3 Hereditary breast cancer............................................................................ 365 18.4 Estrogen receptors and ERBB proteins in breast cancer........................... 373 18.5 Classification of breast cancers ................................................................. 378 Further reading:.................................................................................................. 382 19 Prostate Cancer ................................................................................................ 383 19.1 Epidemiology of prostate cancer................................................................ 384 19.2 Androgens in prostate cancer..................................................................... 389 19.3 Genetics and epigenetics of prostate cancer .............................................. 394 19.4 Tumor-stroma interactions in prostate cancer........................................... 398 Further reading................................................................................................... 402 PART III - PREVENTION, DIAGNOSIS, AND THERAPY 20 Cancer Prevention ............................................................................................ 403 20.1 The importance of cancer prevention......................................................... 403 20.2 Primary prevention..................................................................................... 404 20.3 Cancer prevention and diet ........................................................................ 408 20.4 Prevention of cancers in groups at high risk.............................................. 415 20.5 Prevention of prostate cancer by screening the aging male population.... 420 20.6 Other types of prevention ........................................................................... 423 Further reading................................................................................................... 426 x 21 Cancer Diagnosis .............................................................................................. 427 21.1 The evolving scope of molecular diagnostics............................................. 427 21.2 Molecular diagnosis of hematological cancers.......................................... 429 21.3 Molecular detection of carcinomas ............................................................ 433 21.4 Molecular classification of carcinomas ..................................................... 439 21.5 Prospects of molecular diagnostics in the age of individualized therapy.. 442 Further reading................................................................................................... 447 22 Cancer Therapy ................................................................................................ 449 22.1 Limitations of current cancer therapies ..................................................... 449 22.2 Molecular mechanisms of cancer chemotherapy ....................................... 450 22.3 Principles of targeted drug therapy............................................................ 459 22.4 Examples of new target-directed drug therapies........................................ 464 22.5 New concepts in cancer therapy: Immunotherapy ..................................... 475 22.6 New concepts in cancer therapy: Gene therapy......................................... 479 22.7 The future of cancer therapy ...................................................................... 486.