Nonbreast second malignancies after treatment of primary breast cancer

To determine the incidence and risk factors for nonbreast second malignancies (NBSMs) in women after treatment for primary breast cancer.

Between January 1985 and December 1995, a total of 1,084 breast cancer patients were analyzed for NBSMs. Detailed analysis was carried out for age, family history, disease stage, radiation therapy, chemotherapy, hormone therapy, other clinical/pathologic characteristics, and site of NBSMs. The Cox proportional hazard regression model was used to estimate the relative risk of NBSMs.

Median follow-up was 12 years. In total, 33 cases of NBSMs were noted in 29 patients. The overall incidence of NBSM was 3%, and the median time for NBSMs was 7 years. The most common NBSMs were gynecologic (22 patients), gastrointestinal (4 patients), head and neck (3 patients), hematologic (2 patients), lung (1 patient), and thyroid (1 patient). The NBSMs rate at 12 years was 2.4% for both mastectomy and radiation therapy groups. In the subset of patients less than 45 years of age at the time of treatment, the NBSMs rate was 0.7% as compared with 4.6% in patients more than 45 years of age (p = 0.001). Statistically significant higher incidences of endometrial and ovarian cancer were seen in patients with hormonal therapy (5.2%) as compared with patients without hormonal therapy (1.8%, p = 0.002). Women with a family history of breast cancer had a higher incidence (6%) of endometrial and ovarian malignancy compared with women without such a history (2.1%, p = 0.003). Chemotherapy did not affect the risk of second malignancy.

The most common NBSMs in this study were gynecologic. Family history of breast cancer was a high risk factor for NBSMs. No risk of NBSMs with radiotherapy was observed.