Clinical course and treatment outcomes in solid-basaloid adenoid cystic carcinoma of the breast: A systematic review and case report

Background Adenoid Cystic Carcinoma (ACC) is a rare, indolent subtype of triple-negative breast cancer, accounting for < 0.1 % of cases. The solid-basaloid subtype (SBACC), comprising approximately one-quarter of breast ACCs, has a poorer prognosis. While ACC is typically managed with surgery and is chemo-resistant, SBACC is more aggressive and often treated with chemotherapy and, more recently, immunotherapy—though supporting evidence remains limited. Aim To assess clinical characteristics and treatment outcomes of SBACC of the breast. Methods This study presents a case of breast SBACC and a systematic review of five databases (inception–September 10, 2024). Eligible studies reported clinical course, treatment, and outcomes. Exclusions included duplicates, non-SBACC focus, animal studies, and those lacking clinical or with only pathological data. Descriptive statistics were used for binary and categorical variables. Risk of bias was assessed using JBI tools, following PRISMA 2020 guidelines. The review is registered in PROSPERO. Results Nineteen studies and one new case (134 patients, aged 19–89) were included. Except for three patients who had with metastatic disease at diagnosis, the rest (97 %) were treated with surgery; 55.6 % received chemotherapy. Among nine patients given neoadjuvant chemotherapy and/or immunotherapy, none achieved complete pathological response, and most had poor outcomes. In non-metastatic cases with reported treatment (n = 99), younger age predicted recurrence (p = 0.032) but not chemotherapy receipt (p = 0.082). Chemotherapy did not reduce recurrence risk (p = 0.819). Mastectomy versus breast-conserving surgery with radiation had similar outcomes (p = 0.197). Conclusions Although limited data are available for this rare cancer, evidence for the efficacy of chemotherapy and immunotherapy for SBACC treatment is lacking. Treatment plans should be individualized to reduce the physical, psychological, and financial burdens on both patients and healthcare systems.