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Adenoid cystic carcinoma of the breast (breast-ACC) is a rare and indolent tumor with a good prognosis despite its triple-negative status. However, we observed different outcomes in the present study. Utilizing the Surveillance, Epidemiology, and End Results (SEER) database, we enrolled a total of 89,937 eligible patients with an estimated 86 breast-ACC cases and 89,851 invasive ductal carcinoma (IDC) patients. In our study, breast-ACC among women presented with a higher proportion of triple-negative breast cancer (TNBC), which was more likely to feature well-differentiated tumors, rare regional lymph node involvement and greater application of breast-conserving surgery (BCS). Kaplan-Meier analysis revealed that patients with breast-ACC and breast-IDC patients had similar breast cancer-specific survival (BCSS) and overall survival (OS). Moreover, using the propensity score matching method, no significant difference in survival was observed in matched pairs of breast-ACC and breast-IDC patients. Additionally, BCSS and OS did not differ significantly between TNBC-ACC and TNBC-IDC after matching patients for age, tumor size, and nodal status. Further subgroup analysis of molecular subtype indicated improved survival in breast-ACC patients with hormone receptor-positive and human epidermal growth factor receptor 2-negative (HR+/Her2-) tumors compared to IDC patients with HR+/Her2- tumors. However, the survival of ACC-TNBC and IDC-TNBC patients was similar. In conclusion, ACCs have an indolent clinical course and result in similar outcomes compared to IDC. Understanding these clinical characteristics and outcomes will endow doctors with evidence to provide the same intensive treatment for ACC-TNBC as for IDC-TNBC and lead to more individualized and tailored therapies for breast-ACC patients.

Breast-conserving surgery (BCS) including radiotherapy (RT) has been demonstrated to provide at least equivalent prognosis to mastectomy in early-stage breast cancer. However, studies on triple-negative breast cancer (TNBC) patients are relatively scarce. The current population-based study aimed to investigate the distinct outcomes between BCS+RT and mastectomy in patients with TNBC. Utilizing the Surveillance, Epidemiology, and End Results (SEER) database, we enrolled 11,514 female TNBC cases diagnosed during the years 2010-2013. Those patients were subdivided into BCS+RT (5,469) and mastectomy groups (6,045), and we conducted a survival comparison between the two groups. The endpoints were breast cancer-specific survival (BCSS) and overall survival (OS). In the overall cohort, patients with BCS+RT exhibited distinctly better breast cancer-specific survival (BCSS) (log-rank, p < 0.001) and overall survival (OS) (log-rank, p < 0.001) than did mastectomy patients. When stratifying the TNBC patients according to age, histology grade, TNM stage, tumor size, and lymph node (LN) status, most patients in the BCS+RT group presented with better survival than did the patients in the mastectomy group, except for the grade I (log-rank, p = 0.830, both BCSS and OS) and stage I (log-rank, BCSS, p = 0.127; OS, p = 0.093) patients. In addition, after adjusting for confounding variables by multivariable Cox proportional hazard analysis, BCS+RT still tended to present with higher BCSS and OS. In conclusion, from our study on SEER data, BCS+RT displayed elevated BCSS and OS in TNBC patients compared to mastectomy, at least equally. Our study provided further evidence for surgeons that BCS with RT is available for TNBC patients.