Causes of Cancer

1.      Intrinsic or predisposing factors

            (i) Heredity- Some chicken are susceptible for leucosis whole others are resistant for leucosis.

            (ii) Age- Neoplasms are more common in old age.

            (iii) Pigmentation- In white horses Melanosarcoma is common. Squamous cell carcinoma is common in Hereford cattle.

            (iv) Sex- No difference, tumors of genital tract are common in females.

     2. Extrinsic factors

            (i) Physical factors- Radium or UV -rays, X-rays, ionizing radiation

            (ii) Chemical factors

                 A. Initiators

            1. Coal-tar

            2. Naturally occurring products e.g. Aflatoxins,

            3. Alkylating agents e.g. cyclophosphamide, chlorambucil.

            4. Polycyclic aromatic hydrocarbons- Tobacco, smoke, pollutants, methylcholanthrene,    

               banzapyrene, benzanthracene

            5. Aromatic amines- h-naphthylamine bezidine

            6. Azodyes

            7. Acylating agents- acetyl imidazole

            8. Vinyl chloride monomer

            9. Arsenic

            10. Metals- Nickel, lead, cobalt, chromium

            11. Insecticides- Aldrin, Dieldrin, Chlordane

                B. Promoters

            1. Phenols

            2. Hormones- Estrogen

            3. Drugs- Phenobarbital

            4. Artificial sweeteners- Saccharine

            5. Coloring/ flavoring agents, preservatives

           (iii) Virus

            1. Papilloma virus

            2. Polyoma virus

            3. Adeno virus

            4. Poxvirus

            5. Hepdna virus- Hepatitis B virus

            6. Retrovirus

            7. Herpes virus