Multiple primary cancers in Singapore 1968-1978.

The Singapore Cancer Registry has, since its inception, adopted very strict criteria for the registration of multiple primary cancers. This report covers 121 cases registered from 1968 to 1978, which works out to a proportion of 0.5% of all persons with cancer. The strict criteria has ruled out all second primaries in multicentric foci in the same organs or in bilaterally paired organs, thus accounting for the very small number. There were significantly more females, but no significant differences among the three major ethnic groups. The females were generally younger at first diagnosis (mean 54 years) compared to the males (mean 60 years). The time-interval between diagnoses ranged from 0 to 20 years, with the median at 3 years, the interval being longer in younger patients. Interesting site associations include the kidney-bladder and cervix-lung combinations.