1. Carcinogenesis
Carcinogenesis is mostly due to non-lethal genetic damage
Such genetic damage (or mutation) may be acquired by the action of environmental agents, such as chemicals, radiation, or viruses, or it may be inherited in the germ line
The tumour mass results from clonal expansion of a single progenitor cell that has acquired the genetic damage (i.e., tumors are monoclonal)

2. Carcinogenesis Carcinogenesis is a multistep process
A malignant tumour has several phenotypic features, such as excessive growth, local invasiveness, and the ability to form distant metastases
These characteristics are acquired in a stepwise fashion (tumour progression)

4. Carcinogenesis Growth-promoting protoncogenes Tumor suppressor genes
Three classes of normal regulatory genes are the principal targets of genetic damage:
Growth-promoting protoncogenes
Tumor suppressor genes
Genes that regulate apoptosis
In addition, a fourth category of genes, DNA repair genes those regulate repair of damaged DNA, is important in carcinogenesis.

5. Oncogenes
Proto-oncogenes: cellular genes that encode protiens promoting normal cell growth & differentiation
Oncogenes: genes whose products are associated with neoplastic tranformation
Proto-oncogene
Oncogene

8. ETIOLOGY OF CANCER: CARCINOGENIC AGENTS
Three classes of carcinogenic agents can be identified:
Chemicals
Radiant energy, and
Microbial agents.

9. ETIOLOGY OF CANCER: CARCINOGENIC AGENTS
Chemical Carcinogens
Benzo-pyrene produced from cigarette smoking and cause lung cancer .
Polycyclic hydrocarbons produced from boiled animal fats and are present in smoked meats and fish and cause GIT cancer.
Aromatic amines : produce bladder cancers in exposed workers of rubber industries.
Azo dyes used to color food (e.g., butter-yellow to make margarine more enticing and scarlet-red for cherries) and cause GIT cancer.

10. ETIOLOGY OF CANCER: CARCINOGENIC AGENTS
Chemical Carcinogens
Nitrosamines produced formed nitrites that have been added to food as preservatives and cause cancer stomach.
Aflatoxin produced by Aspergillus, a mold that grows on improperly stored grains and nuts. Food contamination lead to hepatocellular carcinoma.
Vinyl chloride, arsenic, nickel, chromium, insecticides, fungicides, all are chemical carcinogens.

11. ETIOLOGY OF CANCER: CARCINOGENIC AGENTS
Radiation Carcinogenesis
Radiation, whatever its source (UV rays of sunlight, x-rays, nuclear fission, radionuclides) is an established carcinogen.
The effect of ionizing radiation is related to its mutagenic effects
Because the latent period of irradiation-associated cancers is extremely long
Natural UV radiation derived from the sun can cause skin cancers (melanomas, squamous cell carcinomas, and basal cell carcinomas). At greatest risk are fair-skinned people.

12. ETIOLOGY OF CANCER: CARCINOGENIC AGENTS
Viral and Microbial Carcinogenesis
Human Papillomavirus (HPV) type 16 &18 cause squamous cell cancers of the cervix and anal, perianal area, vulva, and penis.
Epstein-Barr Virus (EBV) cause Burkitt lymphoma, primary CNS lymphoma in AIDS patients, and nasopharyngeal carcinoma.
Hepatitis B Virus (HBV) chronic HBV infection cause hepatocellular carcinoma.
Hepatitis C virus (HCV) also is strongly linked to hepatocellular carcinoma
Helecobacter pylori bacteria, cause gastric carcinoma and gastric lymphoma.

13. Diagnosis of Cancer Biopsy Fine needle aspiration Cytologic smears
Immunocytochemistry
Tumor markers
Flow cytometry