Multiple primary cancers of separate organ sites: implications for research and cancer control (Australia).

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.