Long-term risk of second malignancies in women with ductal carcinoma in situ or early-stage invasive breast cancer after breast conservation treatment.

e12103 Background: Women with ductal carcinoma in situ (DCIS) or early stage breast cancer have a good prognosis after breast conservation treatment (BCT), and are at risk for second malignant neoplasms (SMNs). The long-term risk of SMNs is not well established and carries important public health implications. Methods: A total of 755 women with DCIS or stage I-II invasive breast cancer underwent breast-conserving surgery followed by definitive breast irradiation between 1995 and 2001. Systemic therapy (chemotherapy and/or hormonal therapy) was given to 73% of the patients. We have previously described patient demographics and 15-year oncologic outcomes in detail (Vapiwala, Cancer, 2017). The patient records were reviewed for development of SMNs. SMNs of any anatomic site (other than contralateral breast cancer and basal/squamous cell carcinoma of the skin) were included for analysis. The Kaplan-Meier method was used to determine the rate of SMNs over time. Median follow-up was 13.8 years. Results: The 5-, 10-, and 15-year rates of developing any SMN were 3.6% (95% CI 2.4-5.3%), 7.8% (95% CI 6.0-10.2%), and 12.7% (95% CI 10.2-15.8%). The most common SMNs were uterine (n=12), leukemia/lymphoma (n=11), melanoma (n=10), ovarian (n=9), and lung (n=7). Conclusions: Development of SMNs is a substantial risk for a protracted period of time following BCT. Clinical patterns of specific SMN histologies, locations and time course of development suggest potential opportunities for screening and treatment to guide patient survivorship clinics and protocols.