Epidemiology of Cancer
Definitions: 1) Carcinogenesis: A process whereby a chemical or physical agent (Carcinogen) causes cancer 2) Teratogenesis: A process whereby a chemical or physical agent (Tetratogen) causes a deformed fetuses 3) Mutagenesis: A process whereby a chemical or physical agent (Mutagen) that changes (Mutation) the genetic material Initiates carcinogenesis and some teratogenesisAbnormal proliferation of cells Benign: not invade surrounding tissues Malignant: invade near and far tissues
Topography code: organ or tissue affected Morphology code: histology features
Incidence rate Mortality rate No. of years of life lostDeath certificate: mortality rate Population based tumor registry : incidence rate
1.AGE: Most adult CA arise from basal epithelial cells of ectodermal or endodermal origin Most childhood CA are of mesodermal origin2.SEXMost major cancers of non-sexual organsare more in males except: CA-thyroidCA –Gall BladderٍSmoking and occupational cancers are more in males
3.RACE AND GEOGRAPHY Great variation between races in the same geographical area and within the same race at various geographical area (migrants)
4.TIME TREND CA-Lung: increasing (increased smoking) CA-Stomach: decreasing (more fresh and frozen than preserved food) CA-Uterus, cervix: decreasing (increased hysterectomy due to non-CA causes) CA-Liver: decreasing (better diagnosis of primary sires) Children CA: decreasing (better treatment) CA-Colon, Rectum, Pancreas, Breast, Prostate, Leukemia: not changed
1.TOBACCO SMOKING Responsible for 30% of CA-deaths Increases risk of: CA-lung by 10 times CA-larynx by 8 times CA-mouth and pharynx by 4 times CA-urinary bladder, renal pelvis, ureter, pancrease by 2 times It also increases risk of CA- renal parenchyma and stomach
Attributable risk % CA-lung:90% CA mouth, pharynx, larynx, esophagus:75% CA-UB:50% CA-pancrease:40%
4700 chemicals in tobacco smoke 43 are carcinogenic (cadmium, benzene) Lung CA epidemic: In men peak 1990s , declining now In women, expected to climb
Responsible for 4% of all male cancer deaths, and 2% of all female cancer deaths It increases risk of : Hepatocellular cancer CA-mouth, pharynx, esophagus, supraglottic cancer It potentiates effect of smoking
Responsible for 5% of all cancersInternational Agency for Research on CancerGroup 1 Human Carcinogen Benzene and TobaccoGroup 2A Probably Carcinogenic AcrylamideGroup 2B Possibly Carcinogenic AcetylaldehydeGroup 3 Unclassifiable Group 4 Not a Carcinogen Caprolactam
Responsible for 1% of all cancer Alkylating agents: AML, CA-UB N2 mustard, Arsenic compounds, methoxolone: CA-skin Phenacetin: CA-UB, Renal Pelvis
Responsible for 1% of all cancer Sources: natural medical consumer External exposure affects: superficial organs (thyroid, breast) Susceptible organs (bone marrow)
Internal exposure: Inhalation of radioactive dust: CA-Lung Ingestion of Radium: Bone tumor Pelvic implants : CA- colon, rectum Exposure to Iodine131: CA-throid
Responsible for 10% of all cancers, and 2% of CA-deaths Sun light : squamous and basal cell Ca of skin, and malignant melanoma Low-frequency electromagnetic field: leukemia and CA-brain
5 mechanisms are involved in the relation between diet and cancer 1st mechanism Ingestion of food contaminated by preformed carcinogen Aflatoxin B and hepatoma Artificial sweetener and bladder cancer
2nd mechanism Provision of substrate for the formation of carcinogens in the body or by altering concentration or duration of contact of carcinogens with colonic mucosaIngested amines and nitrites with CA stomach, bladder, colon and esophagusVitamin C inhibits formation of N-nitroso compounds and decrease risk of CA-stomach and esophagusFiber and CA –colonHigh fat and CA-colon, breast , prostate
3rd Mechanism Induction or inhibition of enzymes that affect carcinogenesis Vegetable of Brassicaceae family and CA colon
4th mechanism Production or prevention of formation or deactivation of short lived carcinogenic molecular species as Free Radicals
5th mechanism Obesity that act as a tumor promoter by excess endogenous estrogen increasing risk of endometerial cancer and postmenopausal breast CA Early menarche and late menopause are related to overnutrition and increased risk of CA breast and endometerium
Responsible for 20% of cancer in developing countries, and 4% in developed countriesDNA virusesEBV-African burket lymphoma, nasopharyngeal cancerHBV-hepatomaHSV-2 –CA cervixHPV- CA cervix, vulva, anus
RNA virusesHIV –kaposi sarcoma, Non-Hodjkin lymphomaHTLV-1,2 –T-cell leukemiaHCV-hepatoma
Schistosoma haematobium- CA-UBClonorchis sinensis-hepatic angiosarcomaOpisthorchis virerrini(liver fluke) –cholangial cancer
Nullipara women have higher risk of CA ovary ,endometrium, and breast Risk of ovarian and endometrial cancer decreases with increasing number of pregnancies Risk of CA-breast increases with increasing age of having first baby
DES increases risk of CA-vagina in female offspring and testicular CA in male offspring Estrogen increases risk of CA endometerium, while progesteron is protective
OC : Decreases risk of ovarian cancer Relation with CA breast is not conclusive Combined OC decreases risk of fibrocystic disease and adenoma Combined OC increases risk of hepatoadenoma, and focal nodular hyperplasia
Very important in the genesis of many forms of CA CA breast and prostate aggregate in families Malignant Melanoma are more in light skinned , red hair, blue eyes individuals CA-stomach is more in individuals with B.groupA
Nasopharyngeal CA is more in individuals with HLA-2A relation between FAP and CA-colonA relation between Xeroderma pigmentosa and CA-skinA relation betwee Bloom”s syndrome and leukemiaWilm”s tumor and retinoblastoma are genetically determined
Advice against all forms of tobacco smoking Advice against alcohol, especially among smokers Reduce exposure to carcinogens in and outside workplace Avoid unnecessary use of suspected carcinogenic drugs
Prudent use of diagnostic X-RayAvoid exposure to sunlight , especially light –skinnedUse minimum dose of estrogen to achieve theraputic effectAvoid giving estrogen to pregnant womenEnhance against female promiscuity, and male homosexuality
Encourage having a diet with low fat and meat but high in fruit , vegetables ,and fibers Advice against obesity Advice for early first full term pregnancy
CXR, and sputum cytology for CA-Lung: not beneficial Urinary cytology for CA-UB: not encouraging results Oral cytology for oral CA: Non-conclusive results Barium meal for CA-stomach: Increased survival in screened but not in general population
Testicular self-exam CA-testes: Not effective Digital rectal exam for CA-rectum, and prostate: Non-conclusive BSE and mammography for CA breast : VERY EFFECTIVE Pap smear for Ca cervix: VERY EFFECTIVE