Retinoblastoma: An Epidemiological Appraisal with Reference to a Population in Mumbai, India

Reliable data on incidence and mortalityfor childhood cancers are available from only a few areas in the developing countries. Neoplasia in children is rare as compared with adult cancer. In Europe, North America and Australia, retinoblastomas account for 2-4 percent of the total and the relative frequency is similar in Asia. In contrast, in African countries retinoblastomas account for 10 to 15% of cancers in children. The data collected at Bombay Cancer Registry for the latest 13 years, 1986-1998, were used for the present study. Analyses were carried out on retinoblastomas by sex, age, religion and laterality, based on differences in rates and proportions. In Mumbai, during the 13-year period in question, there were only 211 cases of malignant tumors of the eyes. Of these, 147 were retinoblastomas, 84 in males and 63 in females, with crude incidence rates per million population of 4.0 and 3.1, respectively. The corresponding age adjusted incidence rates per million population were 4.2 and 3.3. The crude values were found to be higher in Muslims as compared to Hindus and other religious groups, in both sexes. Out of the total retinoblastomas, 105 were localized, 24 demonstrated regional spread and 16 had metastasized or were very advanced. Some 23 patients had bilateral disease. In a total of 60 patients, retinoblastomas developed on the right side and in 58 in the left eye. The highest annual age standardized incidence rates for retinoblastomas, in excess of 7 per million population have been observed in the Fortaleza area of Brazil, Nigeria (Ibadan) and Uganda-Kampala. Retinoblastomas have the lowest median age of all childhood malignancies, approximately 15 months. The male to female ratio generally fluctuates around unity but our data indicated a higher proportion in males. Ethnic differences in the frequencies of unilateral and bilateral retinoblastomas are apparent. There is little evidence that any significant change in the incidence of retinoblastoma over time has occurred in any part of the world. Knudson proposed a 2-mutation hypothesis to explain the occurrence of retinoblastoma in both hereditary and sporadic forms with differing frequencies of bilaterality, and this model has become a paradigm for considering the role of genetic factors in the etiology of cancer in general.