Adenoid Cystic Carcinoma of the Breast: Clinicopathological Features and Long-Term Outcomes from a 20-Year Retrospective Cohort.

Abstract

Background: Adenoid cystic carcinoma (ACC) of the breast is a rare triple-negative malignancy with an indolent clinical course distinct from conventional triple-negative breast cancer (TNBC). Optimal management remains undefined due to limited prospective data. This study aimed to characterise the clinicopathological features, treatment patterns, and long-term outcomes of breast ACC at a high-volume specialist centre, contributing real-world evidence to inform management in the absence of prospective trial data.

Methods: A single-institution retrospective cohort study was conducted of 24 patients with histopathologically confirmed breast ACC treated at The Royal Marsden NHS Foundation Trust between 2000 and 2020. Clinicopathological and outcome data were analysed descriptively; overall survival (OS), disease-specific survival (DSS), and relapse-free survival (RFS) were estimated using the Kaplan-Meier method.

Results: Median age was 57 years. Nodal involvement was rare (8%). Adjuvant radiotherapy was administered in 88% of patients; only two patients (8%) received chemotherapy for breast ACC. Five patients (21%) experienced disease relapse after a median of 2.3 years (range 1.3-14.0). The estimated 5- and 10-year OS were both 88.4% (95% CI 74.5-100%) and DSS were both 93.3% (95% CI 81.5-100%).

Conclusions: To our knowledge this represents the largest single-institution cohort study of breast ACC reported to date. The clinical behaviour of breast ACC more closely resembles salivary gland ACC than conventional TNBC, supporting a conservative locoregionally focused management approach and questioning the routine use of chemotherapy on the basis of triple-negative receptor status alone. The propensity for late relapse supports long-term surveillance beyond the standard 5-year window.