CASE REPORT – INVASIVE DUCTAL CARCINOMA FOLLOWING REMOVAL OF BENIGN BREAST TUMOR IN 93-YEAR-OLD MALE Gavin Crist, OMS-II1, Jeffrey D. Goodwin, OMS-II1, Joseph Davenport, OMS-II1, Ben Brooks, PhD, MBA2 1. College of Osteopathic Medicine, Rocky Vista University, Ivins, UT USA 2. Department of Clinical Education, Rocky Vista University, Ivins, UT USA

Introduction – Invasive ductal carcinoma (IDC) is the most common breast cancer in men but represents less than 1% percent of breast carcinomas diagnosed in the US annually. To date, there is only one identifiable male case reporting carcinoma in the same breast following surgical resection of a benign neoplasm. This case report aims to document an incredibly rare occurrence of IDC in the same location as a previously removed benign neoplasm in a 93-year-old man. Case description – A 93-year-old male presented to the surgical oncologist with newly diagnosed left breast cancer, determined to be IDC by a diagnostic mammogram, ultrasound, and biopsy. He had a long history of lumps on the left side including gynecomastia at age 20, which was treated without surgery, and a lump that was excised in his late 50s, a (patient-reported) teratoma. A left mastectomy and sentinel node biopsy was performed. The tumor was confirmed IDC, grade 2, 2.5 cm, margins >10 mm, negative lymph nodes (0/6), ER positive (strong, 90%), PR positive (strong, 85%), HER2 negative, Ki-67 15%, Magee score 14, stage IIA (pT2N0). The patient reported no postoperative complications with well controlled pain. Discussion – The development of IDC in the same location as a previously resected benign tumor is unusual but highlights the importance of long-term surveillance in patients with a history of breast lesions. The presence of benign precursor lesions, such as atypical ductal hyperplasia (ADH) or ductal carcinoma in situ (DCIS), can increase the risk of subsequent invasive cancer. In this case, the long interval between the benign tumor and the IDC suggests a de novo malignancy rather than a recurrence with transformation. A retrospective cohort study done by Visscher, et al. showed a correlation between benign breast disease (BBD) and breast cancer in women, with 9.4% of BBD becoming breast cancer.1 Although no published studies have identified recurrence rates of benign tumors in men, the recurrence rate in women is between three and six percent.2,3 An estimation of the likelihood of benign recurrence with subsequent transformation would be approximately 0.28-0.56%. Although there is no data available to estimate the probability of breast cancer occurring in the same location as a benign tumor over 30 years post-surgery, there is one other documented occurrence where a benign, resected tumor preceded IDC in a male.4 Conclusion – The scarcity of cases, low likelihood of recurrence with transformation, and long interval between tumors demonstrate the need for consistent vigilance and follow-up care in men with a history of benign breast tumors. References: 1. Visscher DW, Frost MH, Hartmann LC, et al. Clinicopathologic features of breast cancers that develop in women with previous benign breast disease. Cancer. 2016;122(3):378-385. doi:10.1002/cncr.29766 2. Benign and Low-Grade Fibroepithelial Neoplasms of the Breast Have Low Recurrence Rate After Positive Surgical Margins. Cowan ML, Argani P, Cimino-Mathews A. Modern Pathology : An Official Journal of the United States and Canadian Academy of Pathology, Inc. 2016;29(3):259-65. doi:10.1038/modpathol.2015.157. 3. Risk of Local Recurrence of Benign and Borderline Phyllodes Tumors: A Danish Population-Based Retrospective Study. Borhani-Khomani K, Talman ML, Kroman N, Tvedskov TF. Annals of Surgical Oncology. 2016;23(5):1543-8. doi:10.1245/s10434-015-5041-y. 4. Nicosia L, Lissidini G, Sargenti M, et al. Ductal carcinoma in situ of the male breast: clinical radiological features and management in a cancer referral center. Breast Cancer Res Treat. 2022;196(2):371-377. doi:10.1007/s10549-022-06689-y