Purpose The aim of this study was to determine the incidence and risk factors for gynecological cancer as second malignancy (SM) after treatment of breast cancer (BC).

Methods and Materials Between January 1985 and December 2007, a total of 2756 patients with BC were analyzed for gynecological cancers as an SM. Analysis was carried out for patient-, disease-, and treatment-related characteristics. The Cox proportional hazards regression model was used to estimate the relative risk of gynecologic malignancies.

Results The median age at BC diagnosis was 49 years and median follow-up of 14 years. In total, 25 cases of gynecological cancer were noted with an incidence of 0.9%. We observed 9 ovarian and endometrium (0.3%) as well as 7 uterine cervix (0.25%) cancers. Family history of BC was the most significant risk factor for SM (relative risk, 7.4; 95% confidence interval, 3.03–18.28; P<0.001). Women with a family history of BC had a higher incidence of endometrial (12%) and ovarian (16%) cancer compared with those who have no family history (0.1%, P = 0.003). Statistically significant higher incidence of endometrial cancer was seen in patients undergoing hormonal therapy (0.4%) as compared with those who are not undergoing hormonal therapy (0.1%, P = 0.001). Most of the endometrial (88.9%) and cervical (71%) cancers were detected at an early stage but ovarian cancers (66.6%) in advanced stage. Chemotherapy and radiotherapy did not increase the risk of gynecological SM.

Conclusions Women with BC are at risk of developing a second primary gynecological malignancy particularly of endometrium and ovary. Family history of BC was a high risk factor for gynecologic SM. These patients should be followed up for its early detection.