"Cancer GeneticsCancer: Cancer is a class of diseases in which a group of cells display uncontrolled growth,invasion and sometimes metastasis. Most cancers form tumor but some like leukemia do not. Oncology: The branch of medicine concerned with the study, diagnosis, treatment andprevention of cancer is oncology.Cancer genetics: Nearly all cancers are caused by abnormalities in genetic material of thetransformed cells. These abnormalities may be due to effect of carcinogens. Other cancerpromoting genetic abnormalities may be randomly acquired through errors in DNAreplication or are inherited and thus present in all cells from birth. Genetic abnormalitiesfound in cancer typically affect two general classes of genes.1. Cancer- promoting oncogenes:- these are typically activated in cancer cells, givingthose cells new properties, such as hyperactive growth and division, protection againstprogrammed cell death, loss of respect for normal tissue boundaries, and the ability tobecome established in diverse tissue environment.2. Tumor suppressing genes are then inactivated in cancer cells, resulting in the loss ofnormal functions in those cells, such as accurate DNA replication, control over thecell cycle, orientation and adhesion within tissues and interaction with protective cellsof immune system.Classification: Cancers are classified by the type of cells that resemble the tumor andtherefore the tissue presumed to be the origin of the tumor. Examples of general categoriesinclude. ? Carcinoma: Malignant tumors derived from epithelial cells. This group representsthe most common cancers including the common cancers, including the commonforms of breast, prostate, lung and colon cancer.? Sarcoma: Malignant tumors derived from connective tissue, or mesenchymal cells.? Lymphoma and Leukemia:Malignancies derived from hematopoietic (blood- forming) cells.? Germ cell tumor:Tumors derived from totipotent cells. In adults most often found inthe testicle and ovary.Prevalence of adult cancers:MALE FEMALEMost Common Most Common Most Common Most(by occurrence) (By mortality) (by occurrence) Common(Bymortality)Prostate cancer (33%) Lung Cancer (31%) Breast Cancer (32%) Lung Cancer(27%)Lung Cancer (13%) Prostate cancer (10%) Lung Cancer (12%) BreastCancer (15%)Colorectal cancer (10%) Colorectal cancer Colorectal cancer (11%) Colorectal(10%) cancer (10%)Bladder cancer (7%) Pancreatic cancer Endometrial cancer (6%) Ovarian(5%) Cancer (6%)Cutaneous melanoma Leukemia (4%) Non-Hodgkin’s lymphoma Pancreatic(5%) (4%) cancer (6%) Signs and Symptoms:Roughly cancer symptoms can be divided into three groups.1. Local Symptoms? Unusual lump or swelling (Tumor)? Hemorrhage (bleeding)? Pain and/or ulceration2. Symptoms of metastasis (spreading)? Enlarged lymph nodes? Cough and hemoptysis? Hepatomegaly3. Systemic symptoms? Weight loss? Poor appetite? Fatigue? Excessive sweating? Anemia? Hormonal changesFamilial Cancer: Most forms of cancer are “sporadic” and have no basis of heredity.However there are a number of recognized syndromes of cancer with the heredity componentoften a defective tumor suppressor allele. Famous examples are:- ? Certain inherited mutations in the genes BRCA1 and BRCA2 are associated with anelevated risk of breast cancer and ovarian cancer. ? Various tumors such as osteosarcoma, breast cancer, soft tissue sarcoma, brain tumorsetc. occur due to mutation of p53 genes.? Familial adenomatous polyposis an inherited mutation of the APC gene that lead toearly onset of colon carcinoma.? Retinoblastoma, when occurring in young children is due to a hereditary mutation inretinoblastoma genes.Causes of cancer: Cancers are primarily an environmental disease with 90–95% of casesattributed to environmental factors and 5–10% due to genetics. Common environmentalfactors that contribute to cancer death include tobacco (25–30%), diet and obesity (30–35%),infections (15–20%), radiation (both ionizing and non-ionizing, up to 10%), stress, lack ofphysical activity, and environmental pollutants. Some important causes of cancer are:-(i)Chemicals carcinogens: Tobacco smoking is associated with many forms of cancer andcauses 90% of lung cancer. Alcohol is also causes cancer. Millions of workers run the risk ofdeveloping cancers such as lung cancer and mesothelioma from inhaling asbestos fibers andtobacco smoke, or leukemia from exposure to benzene at their workplaces.(ii) Radiation: Up to 10% of invasive cancers are related to radiation exposure, includingboth ionizing radiation and non-ionizing ultraviolet radiation. Prolonged exposure toultraviolet radiation from the sun can lead to melanoma and other skin malignancies. Clearevidence establishes ultraviolet radiation, especially the non-ionizing medium wave UVB, asthe cause of most non-melanoma skin cancers, which are the most common forms of cancerin the world.(iii) Physical agents:Some substances cause cancer primarily through their physical, ratherthan chemical, effects on cells. Prominent example of this is prolonged exposure to asbestos,naturally occurring mineral fibers which are a major cause of mesothelioma, a type of cancer of the serous membrane. Nonfibrous particulate materials that cause cancer include powderedmetallic cobalt and nickel, and crystalline silica (quartz, cristobalite, and tridymite).(iv)Hormones: Some hormones play a role in the development of cancer by promoting cellproliferation. Hormones are important agents in sex-related cancers such as cancer of thebreast, endometrium, prostate, ovary, and testis, and also of thyroid cancer and bone cancer.(v)Heredity: Hereditary cancers are primarily caused by an inherited genetic defect. Lessthan 0.3% of the population is carriers of a genetic mutation which has a large effect oncancer risk and this cause less than 3–10% of all cancer. Some of these syndromes include:certain inherited mutations in the genes BRCA1 and BRCA2 with a more than 75% risk ofbreast cancer and ovarian cancer and hereditary nonpolyposis colorectal cancer (HNPCC orLynch syndrome) which is present in about 3% of people with colorectal cancer amongothers.(vi) Infection:Worldwide approximately 18% of cancer deaths are related to infectiousdiseases. Viruses are the usual infectious agents that cause cancer but bacteria and parasitesmay also have an effect. A virus that can cause cancer is called an oncovirus. These includehuman papillomavirus (cervical carcinoma), Epstein-Barr virus (B-cell lymphoproliferativedisease and nasopharyngeal carcinoma), Kaposi's sarcoma herpes virus (Kaposi's Sarcomaand primary effusion lymphomas), hepatitis B and hepatitis C viruses (hepatocellularcarcinoma), and Human T-cell leukemia virus-1 (T-cell leukemias). Bacterial infection mayalso increase the risk of cancer, as seen in Helicobacter pylori-induced gastric carcinoma.Parasitic infections strongly associated with cancer include Schistosomahaematobium(squamous cell carcinoma of the bladder) and the liver flukes, Opisthorchisviverrini andClonorchissinensis (cholangiocarcinoma). "