Second primary in the contralateral breast after treatment of breast cancer

To study the potential risk factors for contralateral breast cancer (CBC) in women after treatment of the primary breast cancer.

Between January 1985 and December 1995, records of 1084 breast cancer patients at our institution were analyzed for incidence of CBC. In all the patients a detailed analysis was carried out with respect to age, disease stage, radiation therapy technique, dose, the use of chemotherapy or hormone therapy, and other clinical and/or pathologic characteristics. The Kaplan-Meier method was used to estimate the acturial rate of CBC. The Cox proportional hazard regression model was used to estimate the relative risk (RR) of CBC.

Up to December 2005, the median follow up was 12 years. Overall incidence of CBC was 4%. The 10 and 20 year acturial rate of CBC was 5.6% and 11.3%, respectively. The CBC rate at 10 and 20 year was 5.4% and 10.2%, respectively, for patients with mastectomy only and 5.1% and 9.7%, respectively, in the mastectomy plus RT group (p=0.3). In the subset of patients <45 years of age at the time of treatment, 10 and 20 year acturial rate of CBC was 5% and 9%, respectively, for patients who underwent mastectomy only and 6.3% and 11%, respectively, for patients treated with mastectomy plus RT (RR=1.4, 95% CI: 1.14-1.45, p=0.003). There was statistically significant lower rate of CBC in patients given adjuvant hormonal therapy (8.5%) as compared to those without hormonal therapy (14.3%, p=0.004) at 20 year. Women with family history of breast cancer had highest rate (15.3%) of CBC (RR=1.6, 95% CI: 1.12-1.27) at 20 years. The adjuvant use of chemotherapy did not significantly affect the risk of second malignancy.

There seems to be little risk of second malignancies in patients treated with mastectomy plus RT using modern techniques, compared with mastectomy only, that was only prevalent in patients <45 years of age. Family history of breast cancer seems to be the highest risk factor for CBC.