CANCER INCIDENCE IN THE FIRST-DEGREE RELATIVES OF OVARIAN-CANCER PATIENTS

Cancer incidence was studied among 3072 first-degree relatives of 559 unselected ovarian cancer patients. Among cohort members there were 30 6 cancer cases. The overall cancer incidence was not increased: the st andardised incidence ratio (SIR) in males was 0.9 (95% confidence inte rval 0.8-1.1) and in females 1.0 (0.8-1.1). The female relatives had a significantly increased risk for ovarian cancer (SIR 2.8, 1.8-4.2). T he excess was attributable to sisters only (SIR 3.7, 2.3-5.7). The rel ative risk for ovarian cancer among sisters decreased both by increasi ng age of the sister add by increasing age at diagnosis of the index p atient: the SIRs were 7.3 (1.5-21.4), 4.5 (1.6-9.8) and 3.1 (1.7-5.4) for sisters of index patients diagnosed in age <45; 45-54 and 55-75 ye ars respectively. The age dependency of the risk supports the role of genetic factors in familial ovarian cancer. Although the risk of ovari an cancer among sisters from Families with breast cancer (SIR 9.2, 3.7 -19.0) was significantly higher than among sisters from families with no breast cancer patients (SIR 2.9, 1.6-4.8, rate ratio 3.1, P < 0.05) , the excess was not solely attributable to coaggregation of breast an d ovarian cancer. Among the 27 families with two or more ovarian cance rs, only sisters were affected in 24 families. which might implicate r ecessive inheritance or shared environmental factors influencing ovari an cancer risk in sisters.