Lifetime risk and trends in lung cancer incidence in greater Mumbai

To estimate the probability of developing lung cancer in the entire life span of the people of Greater Mumbai and variation according to age and sex. Information on cancer incidence trends in a community forms the scientific basis for planning and organising prevention, diagnosis and treatment. During the last 24 year period, a total of 11,458 lung cancer cases were registered (9,052 male and 2,406 female) by the Bombay Cancer Registry. Lung cancer accounts for 9.4% of all male cancers and 2.7% of those in females (6.2% of all cancers) in Greater Mumbai. The probability of developing cancer in the entire life span of the people of Greater Mumbai was estimated.

A method based on the cumulative risk of cancer was used to estimate the probabilities using lung cancer data collected by the population-based Bombay Cancer Registry from the years 1982 to 2005. For evaluation of trends, a linear regression model based on the logarithm of the observed incidence rates was applied. The annual percentage change was also computed for the evaluation. The cumulative incidence rate percentage was calculated by adding up the age-specific incidence rates at single ages and then expressed as a percentage.

The results show that age-adjusted incidence rates of lung cancer during the period 1982 to 2005 showed a statistically significant decreasing trend in males and a statistically significant increasing trend among females. When these trends were examined across different age-groups (0-39, 40-64 and 65 or older), the rates showed a statistically significant decreasing trend from 0-64 years in males and a statistically significant increasing trend in females aged 65 years and older. The rates proved stable across the other age-groups. The probability estimates indicate that one out of every 74 men and one out of every 242 women will contract lung cancer at some time in their whole life in the absence of other causes of death, assuming that the current trends prevail over the time period. Most of them will acquire the disease after the age of 40 years, after which risk increases with time.

The variation in age-adjusted incidence rate across different age-groups in both sexes clearly indicate that there has been a change in the etiology of lung cancer in Greater Mumbai 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 of general interest because changes in diagnostic practices are confounders in time trends of lung cancer in many developed countries, preventing inferences on changes in risk factors.