Purpose: To study the potential risk factors for contralateral breast cancer (CBC) in women after treatment of the primary breast cancer.
Patients and methods: 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.
Results: 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.
Conclusion: 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.