1. GENETIC AND CANCER DECEMBER 2013 K. ETEMADI MAY 2009 K.Etemadi

2. CANCER GENETICS  All cancer is a genetic disease of somatic cells because of aberrant cell division or loss of normal programmed cell death, but a small proportion is strongly predisposed by inherited germ line mutations behaving as Mendelian traits. This does not contradict our traditional understanding that for many cancers environmental factors are of primary etiological importance, whilst heredity seems to play little or no part.  As a general principle it is now clear that cancers arise as the end result of an accumulation of both inherited and somatic mutations in proto-oncogenes and tumor suppressor genes.

3. Differentiation between Genetic and environmental factors in cancer  Epidemiologic studies  Family studies  Twin studies  Disease association  Viral factors

4. Viruses Viruses—mostly in the form of DNA viruses—have been causally linked to cancer.  human papillomaviruses—primarily types 16 and 18, which are sexually transmitted—have been linked to cervical cancer;  more than 25 other types of papillomaviruses have been linked to cancer as well  hepatitis B and C—linked to cancer of the liver  human immunodeficiency virus (HIV)—linked to sarcoma and lymphoma  retroviruses—linked to cancers in animals other than humans

5. Cancer terminology Benign tumours  are generally slow growing and enclosed in a fibrous capsule  are relatively innocuous, although their location can make them serious (such as a tumour located in the brain)  are not considered cancerous (that is, they are not malignant) Malignant tumours  proliferate rapidly, invading neighbouring tissues  can metastasise, or spread, to other sites of the body  are named using the conventions of tissue, cell type, and origin e.g. A tumour of the bone is an osteoma if benign and an osteosarcoma if malignant

6. Cancer terminology Classification by tissue type:  carcinoma epithelial Tissue  (Intestine,Bronchi,mammary ducts)  90% of all tumours derived from ectoderm (mostly) or endoderm (some)  sarcoma Mesenchymal tissue (Bone,muscle,or conective tissue)  2% of all tumours derived from mesoderm  leukaemia circulatory or lymphatic 8% of all tumours derived from mesoderm

7. Types of genes which may mutate to cause cancer :  Tumour suppressor genes  Proto oncogenes  Telomerase

8. Tumour suppressor genes  The gene’s normal function is to regulate cell division. Both alleles need to be mutated or removed in order to lose the gene activity.  The first mutation may be inherited or somatic.  The second mutation will often be a gross event leading to loss of heterozygosity in the surrounding area.

9. CANCER GENETICS  TUMOR SUPPRESSOR GENES The study of hereditary cancer in humans has revealed the existence of what are known as tumor suppressor genes. Studies,which involved fusion of malignant cells with nonmalignant cells in culture, resulted in the suppression of the malignant phenotype in the hybrid cells. The recurrence of malignant phenotype (loss of certain chromosomes from the hybrid cells) suggested that normal cells contain a gene(s) with a tumor suppressor activity. If lost or inactive, can lead to malignancy. That was acting like a recessive trait. The paradigm for our understanding of the biology of tumor suppressor is eye tumor retinoblastoma.further somatic mutation at one or more loci is necessary and environmental factorsTsuch as ionizing radiation

10. Retinoblastoma  Retinoblastoma (RB) is a malignant tumor of the developing retina that occurs in children, usually before the age of five years.  All forms of retinoblastoma represent a mutation in the gene RB1 located in in the region 13q14.1-q14.2.  The gene is about 180 kb in length with 27 exons that code for a transcript of only 4.7 kb.  individual mutations are heterogeneous: 20% are deletions larger than 1kb; 30% are small deletions or insertions; 45% are point mutations.  mutations have been found in 25 of the 27 coding exons and in promoter elements.  (mean of less than 2 tumor foci)

11. CANCER GENETICS - TUMOR SUPPRESSOR GENES  RETINOBLASTOMA Retinoblastoma (Rb) is a relatively rare, highly malignant childhood cancer of the developing retinal cells of the eye that usually occurs before the age of 5 years. Rb can occur either sporadically (non-hereditary form, ussually involve only one eye), or be familial (hereditary form, more commonly bilateral), which is inherited in an AD manner, and also tend to present at an earlier age. ‘Two-hit’ hypothesis – in 1971, Knudson proposed, that affected individuals with a positive family history had inherited one non-functional gene that was present in all cells of the individual (germline mutation), with the second gene at the same locus becoming inactivated somatically in a developing retinal cell. The second mutation was likely given the large number of retinal cells, explaining the AD patterns. It was recognized by cytogenetic analysis of blood samples that about 5% children revealed also interstitial deletion on chromosome 13 (13q14). Tumor material of these children with Rb showed the loss of an allele at the Rb locus – what is known as loss of heterozygosity (LOH). LOH can occur through several mechanisms (loss of a chromosome,a deletion, cross-over between the two homologous genes leading to homozygosity for the mutant allele. In contrast, in the non-heritable form, two inactivating somatic mutations would need to occur independently in the same retinoblast. The Rb tumor will only occur when both RB1 genes are mutated.

12. Knudsen’s “two hit” hypothesis

14. Two hit hypothesis All cells in the hereditary form have one mutated copy of the gene RB1, i.e. the mutation is in the germline.

15. Two-hit hypothesis In the non-hereditary form a mutation in RB1 gene arises as a post-zygotic (somatic) event sometime early in development.

16. © 2005 Elsevier Section of an eye shoving a retinoblastoma in situ.

18. LOSS OF heterozygocity(LOH)

20. p53  suppresses progression through the cell cycle in response to DNA damage  initiates apoptosis if the damage to the cell is severe  acts as a tumour suppressor  is a transcription factor and once activated, it represses transcription of one set of genes (several of which are involved in stimulating cell growth) while stimulating expression of other genes involved in cell cycle control

21. Tumor suppressor Genes in Autosomal dominant cancer syndrome  Li-Fraumeni Syndrome  Retinoblastoma  Neurofibromatosis,type1  Familial breast cancer due to mutation in BRCA1 and BRCA2

22. Gene locations that Causes Heriditary Cancers  Early onset familial breast cancer 17q  Familial adenomatous polyposis 5q  Retinoblastoma – Rb gene 13q  Familial melanoma 9p  Li- Fraumeni syndrome 17p  Wilms tumor 11p

23. Li- Fraumeni Syndrome  As mutation in Tp53 appear to be a common event in the genetic of many cancers,an inherited or germline mutation of Tp53 woud be expected to have serious consequences.Members of families with this rare syndrome that inherited as an AD trait,are highly susceptible to developing a variety of malignancy at a early age.Point mutations in highly conserved region of the Tp53 gene identified in the germ line of family members

24. CANCER GENETICS - ONCOGENES  ONCOGENES Oncogenes are the altered forms of normal genes – proto-oncogenes –that have key roles in cell growth and differentiation pathways. In normal mammalian cells there are sequences of DNA that are homologous to viral oncogenes, and it is these that are named proto-oncogenes or cellular oncogenes. Although the terms proto-oncogene and cellular oncogene are often used interchangeably, strictly speaking proto- oncogene is reserved for the normal gene and cellular oncogene, or c-onc, refers to a Mutated proto-oncogene, which has oncogenic properties like the viral oncogenes, or v-onc. Some 30 oncogenes have been identified.  IDENTIFICATION OF ONCOGENES Chromosome aberrations are common in malignant cells (variation in chromosome number and structure). Certain chromosomes seem to be more commonly involved. It has been found that chromosomal translocation can lead to novel chimeric genes with altered biochemical function or level of proto-oncogene activity.

25. oncogenes  Cellular oncogene c-onc  Viral oncogene v-onc  Proto-oncogene, activated by mutation to c-onc

26. CANCER GENETICS  FUNCTION OF ONCOGENES Cancers have characteristics that indicate, at cellular level, loss of the normal function of oncogene products consistent with a role in the control of cellular proliferation and differentiation in the process known as signal transduction. It is a complex multistep pathway from the cell membrane, through the cytoplasm to the nucleus. Proto oncogenes have been highly conserved during evolution, and the protein products they encode are likely to have essential biological functions.  TYPES OF ONCOGENES 1. Growth factors 2. Growth factors receptors 3. Intracellular signaling transduction factors Proteins with GTPase activity Cytoplasmic serine threonine kinases 4. DNA-binding nuclear proteins 5. Cell cycle factors

27. Activation of oncoges by chromosome translocation  Chronic Myelogenous Leukemia  Burkitt Lymphoma  Acute lymphoblastic leukemia  Acute lymphocytic leukemia  Acute Promyelocytictic leukemia

29. CANCER GENETICS  Chronic myeloid leukemia(CML) In 1960, investigators in Philadelphia were the first to describe an abnormal chromosome(Ph1) in white blood cells from patients with Cml. The abnormal chromosome was found in blood or bone marrow cells but not in other tissues from these patients. The Ph1 is a tiny chromosome – now known to be a chromosome 22, from which material from the long arm has been reciprocally translocated to and from the long arm of chromosome 9 i.e. t(9;22)(q34;q11). This chromosomal rearrangement is seen in 90% of persons with Cml. This translocation has been found to transfer cellular ABL (Abelson) oncogene from chromosome 9 into a region of chromosome 22 known as the break-point cluster, or BCR, region, resulting in a chimeric transcript derived from both the c-ABL (70%) and the BCR genes. This results in a chimeric gene expressing a fusion protein (with transforming activity) consisting of the BCR protein at the amino end and ABL protein at the carboxy end.

30. The "Philadelphia chromosome" 30

31. © 2005 Elsevier Karyotype from a patient with Cml, showing the chromosome 22(arrowed) or Philadelphia chromosome that has material translocated to the long arm of one of the number 9 chromosome (arrowed).

32. Cytogenetic change in cancer(colorectal) Cancer karyotype Stable karyotype

33. EPIGENETIC and CANCER

34. GENETIC OF COMMON CANCER  It is estimated that about 5% of colorectal and breast cancers arise as a result of an inherited cancer susceptibility gene. A similar proportion of many other cancers are due to inherited predisposing genetic factors. But there are some notable exceptions, where only very low incidences of dominantly inherited carcinomas are recorded These include the lung and cervix, leukemias, lymphomas. Here external agents or stimuli are presumably the main factors.

35. Multi-step Theory  Stage of initiation  Latent stage  Stage of promotion  Stage of malignant transformation

36. Transformation is a multistep process

37. Multi-Step Carcinogenesis NormalepitheliumHyper-proliferativeepitheliumEarlyadenomaLateadenomaCarcinomaMetastasis Loss of APCActivation of K-ras Loss of 18q TP53Otheralterations Inter-mediateadenoma

38. Amodel for the step production of colon cancer

39. Colorectal Cancer  11% of cancer-related deaths  Tumor progression may take 10- 35 years  Adenomatous polyp develops into carcinoma

40. Number of Mutation Associated with Some Cancers Cancer Chr. Site No. of Mutation Required ___________________________________ _____ Retinoblastoma 13q 2 Wilms Tumor 11p 2 Colon Cancer 5p, 12p, 17p, 18q 4- 5 Small- Cell Lung 3p, 11p, 13q, 17p 10- 15 Cancer

41. GENETICS OF COMMON CANCERS BREST CANCER  BREAST CANCER is the most common cancer in women between 40 and 55 years of age. Fifteen to 20% of women who develop breast cancer have a family history of the disorde  Approximately 40-50% of families with early-onset autosomal dominant breast cancer have a mutation in the BRCA1 gene (chrom.17q). A mutation in the BRCA1 gene also increases risk of developing bowel cancer, ovarian cancer and prostate cancer.  Mutations in the BRCA2 gene account for 30-40% of families with early-onset AD breast cancer, but were not thought to be associated with increased risk of other cancers.  In some of the original families with familial breast cancer had males who developed breast cancer. Males with mutations in the BRCA2 gene have been shown to have a 6% lifetime risk of developing breast cancer.

42. breast cancer  her age,  family history,  age at which she began menstruating,  whether she has given birth and her age at the time of the first birth, and  whether or not a breast biopsy was performed in the past. Within the general population, there is an 11% chance that any woman will develop breast cancer over her lifetime. For any one individual, this risk may be increased or decreased by a variety of factors:

43. OVARIAN CANCER  Approximately 1 in 70 women develops ovarian cancer,the incidence increasing with age.studies shown a high frequency of LOH at 11q25 in tumor tissues.Mutation in BRCA1,BRCA2 HNPCC,will be responsible for a proportion of these families

44. PROSTATE CANCER  Is the most common cancer affecting men being the most common cancer after breast,with men having a life time risk of 10% of developing prostate cancer and a 3% chance of dying from it.LOH showed at several chromosome location.A small proportion of familial prostate cancer is associated with BRCA1 or BRCA2.Men who carry mutations in BRCA1 or BRCA2 have an increasde risk.Screening by measuring prostate specific antigen (PSA) levels have been sugested.

45. GENETIC COUNSELING IN FAMILIAL CANCERS  Features suggestive of an inherited cancer susceptibility syndrome in a family:  Several close(first or second degree)relatives with a common cancer  Several close relative with related cancers,e.g.breast cancer and ovary cancer  Two family members with the same rare cancers  An unusual early age of onset  Bilateral tumors in paired organs  Synchronous or successive tumors  Tumors in two different organ system in one individual

46. Inherited cancer predispoing syndromes  Families have been described in which cancer occure at more than one site in an individual or at different sites in various members of the family whoud be expected.  The majority of the rare inherited familial cancer currently recognized are dominant inherited.  There are also a number of syndromes usually inherited as autosomal recessive disorders with an increased risk of developing cancer associated with an increased number of abnormalities in the chromosomes that known as the chromosomal brakage syndrome(bloom,fancony,and Xeroderma pigmentosa with SCE)

47. SCREENING FOR FAMILIAL CANCER  Prevention or early detection of cancer is the ultimate goal of screening individuals at risk of familial cancers.  Familial cancer-predisposing syndromes,are inherited as autosomal dominant trait that are fully penetrant,with cosequent risk for heterozygotes of developing cancer approximately100%,this level of risk means that more invasive means of screening with more frequent and earlier initiation of screening protocole are justified

48. Principles of Screening Properties of a good screening test - The test shoud detect a malignant or pre malignant codition at a stage prior to its producing symptoms,with high sensevity and specifity - Accurate and reproducible - Must be an important public health problem - Early detection and intervention must improve outcome - High morbidity and / or mortality associated with disease condition if not treated - Have an accepted treatment for those identified - Non invasive - Has a good statistical profile - Adequate provision for presenting counseling and follow-up shoud be available

49. WHAT age and how often  Most cancer screening programs don’t start until 25 years of age or later.  The highest risk age band for most inherited susceptibilities as 35-50 years  Recommended that screening of at risk individuals 5 years before the age of anset in the earliest affected member of the family  In colorectal cancer is thought that 5-yearly screening intervals is suffice.If however a polyp is found,then the interval between screening down to 3 years.  Braest cancer isnot detectable in premalignant satage and early diagnosis is critical if there is to be a good prognosis.  Annual mammography for females at high risk is therefor recommended from the age of 35

50. What site shoud be screened?  Inherited susceptibility for the common cancers  Colorectal cancer:Colonoscopy is the perfected screening method.Minimal criteria suggest a familial form of colon cancer:1.At least 3 affected relatives(first degree),one a first degree relative of the other two;FAP excluded 2.At least two successive generation affected 3. Cancer diagnosed before age 50 in at least one relative  BREAST CANCER:Mammography is usually only offered to women at incraesed risk of the breast cancer after the age of 35 years,As a cosequence,women at risk of developing breast cancer shoud be taught breast self examination and undergo regular clinical examination  OVARIAN CANCER:In the early stages is frquently asympatic and often incurable by the time a woman presents with symptoms.Early diagnosis is vital.Ultrasound imaging provides the most sensetive means of screening.Measuring the levels of CA125,an antigenic determinant of a glycoprotein that is present in increased levels in the blood of women with ovarian cancer and endometriosis thus not specific for ovarian cancer

51. Cancer and environment: Some environmental agents associated with cancer are:  Viruses  Tobacco smoke  Food  Radiation  Chemicals  Pollution

53. Tobacco smoke  is associated with 50% to 60% of all cancer deaths  is causally linked to cancers of the lung, upper respiratory tract, oesophagus, bladder, pancreas  is probably a cause of cancer of the stomach, liver, kidneys, colon, and rectum

54. Food  is connected to 50% to 60% of cancer deaths  is causally linked to cancers of the lung, upper respiratory tract, oesophagus, bladder, pancreas  is probably a cause of cancers of the stomach, liver, kidneys, colon, and rectum

55. Radiation  UVB from the sun can damage DNA and is associated with more than 90% of skin cancers, including melanomas  radon has been associated with lung cancer among those who work in mines; general levels of radon have not posed a significant cancer threat  electric and magnetic fields from power lines and household appliances have not been demonstrated contributors to the incidence of cancer or leukaemia  radio frequency electromagnetic radiation from mobile phones or microwave ovens has not been linked to cancer.  nuclear radiation is of sufficient energy to ionise molecules and is therefore carcinogenic.

56. Chemicals  benzene (myelogenous leukaemia)  arsenic containing pesticides (lung cancer)  polychlorinated biphenyls (liver and skin cancers)  mineral oils (skin cancer)  mineral fibres (lung cancer and mesothelioma) Chemicals, many of which have been historically linked to the workplace, have been successfully limited through public health efforts, because they have been associated with a variety of cancers. Examples of common chemicals that fall in this category are:

57. Pollution Pollution has been difficult to document as a contributor to human cancer. However, long-term exposure to high levels of air pollution may increase lung cancer risk by as much as 25%.

58. ELEMENTS