Objective: To identify cancers which occur as second primaries following the diagnosis of cancers of other sites, as a basis for formulating causal hypotheses and planning medical surveillance.
Methods: Analyses of fifteen common cancer sites were undertaken to examine the occurrence of multiple primaries. These cancers were notified to the South Australian Cancer Registry during 1977-2001. Historic cohort models were used where standardised incidence ratios (95 confidence limits) were calculated to indicate the risk of second primary cancers.
Results: New associations detected included an increased risk of cancers of the bladder, colon, rectum, kidney and melanomas following a diagnosis of prostate cancer and an increased risk of leukaemia following both lung and rectal cancer. Many previously identified combinations of multiple primaries were confirmed.
Conclusions: From the wide range of associations identified, some such as leukaemias occurring as second primaries after the diagnosis of ovarian cancers and lymphomas may be a treatment effect. The diagnosis of multiple primary cancers in the same month (e.g. bladder-prostate cancers and ovarian-uterine cancers) may reflect patterns of medical testing and the long preclinical phases of some cancers.