Background: The incidence of ductal carcinoma in situ (DCIS) has increased, resulting in more women undergoing post-treatment surveillance for second breast cancers. National Comprehensive Cancer Network (NCCN) guidelines recommend annual breast imaging and physical exam every 6-12 months for five years, and then annually. We assessed mode of detection (imaging, patient-reported, or physical exam) of secondary DCIS and/or invasive breast cancer in a large cohort of DCIS patients undergoing surveillance after treatment of primary DCIS. Methods: We performed a retrospective cohort study of DCIS patients treated between 1/1/2008 and 1/1/2011 within a large integrated health care system. Patients had a minimum of 5 years of follow up. Patient demographics, treatment for primary DCIS, and tumor characteristics (of both primary DCIS and secondary cancer) were obtained from the electronic health record or from manual chart review. Chart review also included mode of detection of secondary breast cancers. Results: Our study cohort consisted of 1561 women with DCIS, with a median age of 59 years (range 32-92) at time of diagnosis. Among initial DCIS tumors, tumor grade was low/intermediate in 942 (60.3%) and high in 619 (39.7%); 1274 (81.6%) were estrogen receptor positive, and 988 (63.3%) progesterone receptor positive. Surgical treatment for the initial DCIS included lumpectomy (n=1134, 72.6%), unilateral mastectomy (n=320, 20.5%), or bilateral mastectomy (n=61, 3.9%), and included sentinel lymph node biopsy in 211 (14%) of patients. Additionally, 691 (44.3%) received radiation therapy and 440 (28.2%) received endocrine therapy. The cohort was followed for a median of 120 months, during which we identified 179 women (11.5%) with a secondary cancer detected at a median time of 57 months. Of the second breast cancers, 77 (43.0%) were ipsilateral, 98 (54.8%) contralateral, and 4 (2.2%) presented with distant metastases; 110 (61.5%) were invasive, 65 (36.3%) were DCIS, and 4 (2.2%) Paget’s disease. See table for mode of detection of second breast cancers. Conclusions: In our cohort of patients undergoing surveillance following initial diagnosis and treatment of DCIS, 2% of secondary breast cancers were detected by clinical breast exam, a rate similar to incidental detection at time of plastic surgery. These results can help inform future recommendations for surveillance of second breast cancers in DCIS patients.

*Incidentally detected cases were identified on pathology report following plastic surgery procedure