2. CANCER IS A GENETIC DISEASE. Cancer arises because of alterations in the DNA that result in uncontrolled cell proliferation. These alterations involve actual sequential changes in the DNA. This is mutation. They may arise as a consequence of random replication errors, exposure to carcinogens, or faulty DNA repair processes.

While virtually most cancer is genetic, most cancer is not inherited. Certain individuals with cancer have inherited a germline mutation that predisposes them to the cancer. Even then, additional somatic mutations are required for a tumour to develop. In a truly sporadic cancer, all of the mutations responsible for the malignant phenotype arise somatically.

3. RNA and DNA tumour viruses. DNA  tumour viruses are more commonly involved in human malignancy. Human papilloma viruses especially types 16 and 18 cause cervical cancer. Both hepatitis B and hepatitis c viruses cause hepatocellular carcinoma. Epstein-Barr virus causes Burkitt's lymphoma in Africa, and nasopharygeal carcinoma in Asia

4. Cancer genes. In 1914, Boveri hypothesized that cells become malignant either because of overactivation of a gene that promotes cell division or because of loss of function of a gene that normally restraints growth. This hypothesis is correct but not complete. Recently it was proven that defects in DNA repair genes are also involved. Thus we have three classes--oncogenes, tumour supressors and DNA repair genes.