Prognosis stratification and postoperative radiation therapy utilization in adenoid cystic carcinoma of the breast

Purpose: Adenoid cystic carcinoma of the breast (ACCB) is a rare malignancy with a favorable prognosis. Little information exists regarding the impact of postoperative radiation therapy (RT) on survival outcome in patients with ACCB. This study aimed to evaluate the clinical significance of postoperative RT in ACCB. Methods: Data of patients with ACCB were extracted from the Surveillance, Epidemiology, and End Results database (2000-2019). Univariate and multivariable Cox regression analyses were performed to identify prognostic factors. In addition, a nomogram model was constructed and internally validated for discrimination and calibration. The value of postoperative RT was respectively accessed in each risk subgroup according to nomogram-deduced individualized score. Results: A total of 689 eligible patients were included in the analysis. Partial mastectomy was associated with an increased risk of death compared with partial mastectomy plus postoperative RT (P = 0.020), but total mastectomy with or without postoperative RT was comparable (P = 0.624). Then, in-depth analysis was performed for patients receiving breast-conserving therapy (n = 485, the training set vs. the testing set = 340 vs. 145). Age at diagnosis, histological grade, and T stage were identified as prognostic factors for overall survival (OS) (All P < 0.05). A nomogram was constructed to provide predictive accuracy toward individual OS rates of ACCB and to divide patients into different risk subgroups. Notably, compared with non-RT, postoperative RT significantly improved OS in the high-risk subgroup (P = 0.006 for the training set, and P = 0.013 for the overall population) but not in the low-risk subgroup (P = 0.807 for the training set, and P = 0.293 for the overall population), suggesting that these patients may be able to exempt from postoperative RT. Conclusion: A robust and effective nomogram was developed to predict prognosis and assist in treatment decisions in patients with ACCB undergoing partial mastectomy.