Objective: To estimate the probability of developing lung cancer in the entire life span of the people ofGreater Mumbai and variation according to age and sex. Information on cancer incidence trends in a communityforms the scientific basis for planning and organising prevention, diagnosis and treatment. During the last 24year period, a total of 11,458 lung cancer cases were registered (9,052 male and 2,406 female) by the BombayCancer Registry. Lung cancer accounts for 9.4% of all male cancers and 2.7% of those in females (6.2% of allcancers) in Greater Mumbai. The probability of developing cancer in the entire life span of the people of GreaterMumbai was estimated. Methods: A method based on the cumulative risk of cancer was used to estimate theprobabilities using lung cancer data collected by the population-based Bombay Cancer Registry from the years1982 to 2005. For evaluation of trends, a linear regression model based on the logarithm of the observed incidencerates was applied. The annual percentage change was also computed for the evaluation. The cumulative incidencerate percentage was calculated by adding up the age-specific incidence rates at single ages and then expressed asa percentage. Results: The results show that age-adjusted incidence rates of lung cancer during the period 1982to 2005 showed a statistically significant decreasing trend in males and a statistically significant increasingtrend among females. When these trends were examined across different age-groups (0-39, 40-64 and 65 orolder), the rates showed a statistically significant decreasing trend from 0-64 years in males and a statisticallysignificant increasing trend in females aged 65 years and older. The rates proved stable across the other agegroups.The probability estimates indicate that one out of every 74 men and one out of every 242 women willcontract lung cancer at some time in their whole life in the absence of other causes of death, assuming that thecurrent trends prevail over the time period. Most of them will acquire the disease after the age of 40 years, afterwhich risk increases with time. Conclusions: The variation in age-adjusted incidence rate across different agegroupsin both sexes clearly indicate that there has been a change in the etiology of lung cancer in GreaterMumbai over time. The most important reason for this would be decrease in smoking prevalence among males.The other reasons for this have to be explored through risk assessment studies, but these findings may be ofgeneral interest because changes in diagnostic practices are confounders in time trends of lung cancer in manydeveloped countries, preventing inferences on changes in risk factors.
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