Age at diagnosis and multiple primary cancers of the breast and ovary.

This nested case-control study assessed the relationship between a woman's age at the time of her initial primary breast or ovarian cancer diagnosis and the risk of a second primary cancer at the other of these two sites. Multiple primary breast and ovarian cancer cases whose initial breast or ovarian diagnosis occurred in 1970-1989 and a random sample of single primary breast or ovarian cancer controls diagnosed in the same years were identified through tumor registries at Duke University Medical Center and the University of North Carolina. Women diagnosed with an initial primary breast cancer at age < or = 50 years were 4.3 times (95% CI: 1.8-10.6) more likely to have developed a subsequent ovarian cancer compared to those diagnosed after age 50. A relationship between an early age at diagnosis (< or = 50) of ovarian cancer and subsequent diagnosis of breast cancer was not found (odds ratio (OR) = 0.6; 95% CI: 0.2-2.0). Adjustment for stage at diagnosis, treatment, year of diagnosis and length of follow-up using Cox Proportional Hazards modeling techniques supported these relationships, yielding a hazard ratio (HR) for the development of a second primary cancer at the alternate site of 4.6 (95% CI: 1.8-11.5) for women with an initial breast cancer diagnosis and 0.6 (95% CI: 0.2-2.2) for women with an initial ovarian cancer diagnosis. Multiple primary breast and ovarian cancer patients diagnosed with an initial breast cancer at or prior to age 50 may represent a distinct subgroup of women with a germline mutation that confers susceptibility to both breast and ovarian cancers.