• Ping Yu, Peng Liu, Yutian Zou, Xinhua Xie, Hailin Tang, Na Li, Xiaoming Xie, and Feng Ye.
• Department of Breast Oncology, Sun Yat-Sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, China.
• Cancer Med. 2020 Aug 1; 9 (15): 5381-5391.

BackgroundMucinous breast carcinoma (MBC) is a relatively rare pathological type of breast cancer. Compared with mastectomy in MBC, the effect and safety of breast-conserving therapy (BCT) remains unclear. Therefore, we investigated the long-term prognosis of BCT and mastectomy in T1-2 stage mucinous breast carcinoma via the Surveillance, Epidemiology, and End Results (SEER) database.MethodsTotally, 8830 patients who were diagnosed of mucinous breast carcinoma between 2004 and 2014 from SEER database were reviewed retrospectively. Cox proportional hazards model and Kaplan-Meier method were performed for evaluating the relationship between surgical method and prognosis.ResultsOne thousand three hundred and twenty (14.9%) patients underwent mastectomy and 7510 (85.1%) underwent BCT. The median follow-up time was 77 months. There were more non-Hispanic white, married, and younger (<65 years) patients, as well as lower stage of tumor sizes, lymph nodes and more favorable histologic grade, ER positive, and PR positive in BCT group (P < .05). Patients in BCT group had relatively better overall survival (OS) than those in mastectomy group. The risk of death from any cause in BCT group was lower than that in mastectomy group significantly (HR = 0.786, 95% CI: 0.703-0.879, P < .001), while no difference significantly was observed in breast cancer-specific survival (BCSS) between BCT and mastectomy groups. In stratified analysis according to T stage, BCT group had better OS than mastectomy group for patients of T1 stage (HR = 0.679, 95% CI: 0.589-0.781, P < .001) or T2 stage (HR = 0.769, 95% CI: 0.646-0.915, P = .003). In stratified analysis according to the different ages, BCT showed OS benefit in patients at the age of 50-64 years (HR = 0.587, 95% CI: 0.408-0.846, P = .004) and the age of 65-79 years (HR = 0.636, 95% CI: 0.535-0.758, P = .001). For patients younger than 50 years or not younger than 80 years, there was no difference significantly observed in OS between BCT and mastectomy groups (P > .05).While for patients who received BCT, the use of radiotherapy showed OS benefit.ConclusionsThis large population-based study indicated patients who received BCT had better prognosis than those received mastectomy in T1-2 stage MBC, especially in patients at the age of 50-79 years. The use of radiotherapy showed OS benefit in patients receiving BCT. Breast-conserving therapy might be preferred over mastectomy especially in locoregional treatment of T1-2 stage MBC.© 2020 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.

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