Cancers of the upper alimentary and respiratory tracts in Bombay, India: a study of incidence over two decades.

Cancers of tongue, oropharynx and larynx in males have registered a decline in incidence over the last two decades in Bombay. This decline has been shown to be a cohort effect. A synoptic measure of risk in each birth cohort, obtained by estimating site-specific cumulative incidence rate over an appropriate age range, was found useful in assessing the risk differential in successive birth cohorts. The changing pattern in incidence of cancers at several sites viz., tongue, oropharynx, and larynx, where bidi smoking is the predominant risk factor, were in conformity with the pattern expected on the basis of changing tobacco habits in the birth cohorts. However, for other sites, viz., hypopharynx, oesophagus and lung, more detailed information on relevant tobacco habits in the birth cohorts is necessary for interpreting the absence of a consistent trend in successive birth cohorts. The recent trends in per capita consumption by type of tobacco (viz., chewing/bidi/cigarette) suggest an emerging cancer pattern in the country at variance with the pattern expected from the current cancer trends in Bombay. Consequently, it is desirable to direct primary cancer prevention programmes especially to cigarette smokers in urban centres and to both bidi and cigarette smokers in the rest of the country.