[Virus and cancer].

There are at least four viruses tightly associated with human cancer: HTLY-I and HTLY-II with certain leukemias, EBV with lymphomas, BHV with hepatocarcinomas and HPV with genital cancer. In this work we discuss some evidences indicating these associations; in particular we emphasize the characteristics of human papillomavirus (HPV), due to its growing importance in the development of uterine-cervix carcinoma and the mortality of Mexican women. The low percentage of infected individuals that develop these neoplasias and the long latency periods observed indicate that both cellular and environmental factors are involved in tumor induction. Among cellular factors, oncogenes (such as myc) and antioncogenes could play important roles in the induction and development of the malignant phenotype. The understanding of these factors could lead to the development of methods for early diagnosis and therapy of cancer.