Increase in breast cancer incidence among older women in Mumbai: 30-year trends and predictions to 2025

Background: Increasing trends in the incidence of breast cancer have been observed in India, including Mumbai. These have likely stemmed from an increasing adoption of lifestyle factors more akin to those commonly observed in westernized countries. Analyses of breast cancer trends and corresponding estimation of the future burden are necessary to better plan rationale cancer control programmes within the country. Methods: We used data from the population-based Mumbai Cancer Registry to study time trends in breast cancer incidence rates 1976–2005 and stratified them according to younger (25–49) and older age group (50–74). Age-period-cohort models were fitted and the net drift used as a measure of the estimated annual percentage change (EAPC). Age-period-cohort models and population projections were used to predict the age-adjusted rates and number of breast cancer cases circa 2025. Results: Breast cancer incidence increased significantly among older women over three decades (EAPC = 1.6%; 95% CI 1.1–2.0), while lesser but significant 1% increase in incidence among younger women was observed (EAPC = 1.0; 95% CI 0.2–1.8). Non-linear period and cohort effects were observed; a trends-based model predicted a close-to-doubling of incident cases by 2025 from 1300 mean cases per annum in 2001–2005 to over 2500 cases in 2021–2025. Conclusions: The incidence of breast cancer has increased in Mumbai during last two to three decades, with increases greater among older women. The number of breast cancer cases is predicted to double to over 2500 cases, the vast majority affecting older women.