The familial risk of breast cancer in women with endometriosis from Yale series.

OBJECTIVE: Few studies examining the association of endometriosis with the risk of breast cancer. Our goal was to investigate the familial risk of breast cancer in women with endometriosis. DESIGN: Retrospective study. SETTING: University-based endometriosis referral center. PATIENTS: Three hundred fifty-two women with endometriosis and 180 infertile women without endometriosis were studied using laparoscopy between August 1996 and February 2002. The endometriosis group was further subdivided into a group of women with 94 positive and 268 negative family histories of breast cancer. MAIN OUTCOME MEASURE(S): The overall risk of familial breast cancer among first- and second-degree relatives in patients with endometriosis and the association between potential risk factors was estimated by chi(2) and by crude adjusted odds ratios (95% CI). RESULTS: Positive family history of breast cancer was detected in (26.7%) 94/352 of endometriosis group and in (5%) 9/180 of controls. The relative risk of women with endometriosis and positive family history of breast cancer was (OR=6.9 (95% CI, 3.4-14.1), chi(2)=34.6, P<0.001). Endometriosis was associated with the risk of first-degree relatives of breast cancer (OR=5.69 (95% CI, 2.4-13.3), P<0.001). Moreover, endometriosis was significantly associated with the risk of breast cancer in mothers (OR=6.3 (95% CI, 2.2-17.8), P<0.001) and in maternal aunts (OR=5.9 (95% CI, 1.3-72.9), P<0.001). The two groups are similar in age, race height, main complaints, age of menarche, cycle length, days of flow, estimated blood loss, stage of endometriosis and the presence of endometrioma. CONCLUSION(S): This study found an elevated risk associated with family history of breast cancer among women with endometriosis. A familial clustering interaction with a familial history of breast cancer in women with endometriosis is possible, but should be investigated further.