A POPULATION-BASED STUDY OF CONTRALATERAL BREAST-CANCER FOLLOWING A FIRST PRIMARY BREAST-CANCER (WASHINGTON, UNITED-STATES)

To evaluate predictors of contralateral breast cancer risk,we examined data from a nested case-control study of second primary cancers among a cohort of women in western Washington (United States) diagnosed wit h breast cancer during 1978 through 1990 and identified through a popu lation-based cancer registry. Cases included all women in the cohort w ho subsequently developed contralateral breast cancer at least six mon ths after the initial diagnosis, but prior to 1992 (n = 234). Controls were sampled randomly from the cohort, matched to cases on age, stage , and year of initial breast cancer diagnosis. Information on potentia l risk factors for second primary cancer was obtained through medical record abstractions and physician questionnaires, Women who were postm enopausal due to a bilateral oophorectomy (i.e., a surgical menopause) at initial breast cancer diagnosis had a reduction in contralateral b reast cancer risk compared with premenopausal women (matched odds rati o [mOR] = 0.25, 95 percent confidence interval [CI] = 0.09-0.68), wher eas no reduction in risk was noted among postmenopausal women who had had a natural menopause (mOR = 0.90, CI = 0.39-2.09). Among postmenopa usal women, there was a suggestion of a lower risk associated with rel atively high parity (2+). A family history of breast cancer was associ ated with an increased risk (mOR = 1.96, CI = 1.22-5.15) and varied li ttle by menopausal status, Having an initial tumor with a lobular comp onent (c.f. a ductal histology) was not related strongly to risk (mOR = 1.47, CI = 0.79-2.74), The results of the present and earlier studie s argue that we have limited ability to predict the occurrence of a co ntralateral breast tumor. Better predictors will be required before di agnostic and preventive interventions can be targeted to subgroups of patients with unilateral breast cancer.