Abstract Introduction: Emerging evidence suggests that triple negative breast cancer (TNBC) is a heterogeneous group comprising biologically distinct subtypes with variable prognoses. Among these, apocrine TNBC represents a rare histological variant characterized by distinct morphological features and molecular profile that may confer a more indolent clinical course. Apocrine TNBC, as defined by the 2019 World Health Organization (WHO) classification, is a special subtype characterized by the absence of estrogen receptor (ER) and progesterone receptor (PR) expression and positivity for androgen receptor (AR). Retrospective cohort studies indicate that patients with apocrine TNBC, often older than 50 years, present with smaller, well- to moderately differentiated tumors compared to other TNBC subtypes. Breast cancer-specific survival (BCSS) and overall survival (OS) are significantly better for apocrine, adenoid cystic, and medullary subtypes compared to metaplastic and NST TNBC. However, data on the response to neoadjuvant or adjuvant chemotherapy in apocrine TNBC remain limited, and clinical decision-making often relies on guidelines developed for NST TNBC. This study aims to describe the clinicopathological characteristics and outcomes of patients with apocrine TNBC. Methods: This is a retrospective, single-center case series. We selected 13 patients with non metastatic apocrine TNBC, EC I, II and III, treated surgically at A.C. Camargo Cancer Center. All patients received neo or adjuvant Cht. Results: The mean age was 59.5 years (range: 35-71 years). All patients (100%) were negative for ER and PR, consistent with TNBC. T1 was the most common stage (N=7, 53.9%), follow by T2 (N=4, 30.7%) and T4 (N=1, 7.7%). The majory was node-negative (N0, N=11, 84.6%), and just one (7.7%) was N+ (N2). The mean Ki67 proliferation index was 33.5% (range: 10-90%). AR high expression in 8 patients (61.5%). 46.2% patient (N=6) had a lower proliferation ki67 of 1-20%, 30.8% patients (N=4) with ki64 between 21-50 and 15.4% (N=2) with ki67 50%. Histologic grade (GH) was II in 7 patients (53.8%) and III in 4 patients (30.8%). Surgical interventions included breast-conserving surgery in 7 patients (53.8%) and mastectomy in 6 patients (46.2%). All pacients received neoadjuvant or adjuvant chemotherapy. Neodjuvant was administered in 3 patients. Among these, one achieved pCR, while the others were staged as ypT2ypN2 and ypT0ypN1. Local recurrence and distance metastasis occurred in 1 patient (7.7%), while 10 patients (76.9%) had no recurrence. The metastatic site was the contralateral breast, and both cases (local recurrence and contralateral breast) were treated with mastectomy. At the last follow-up, 12 patients (92.3%) were alive without disease, with 1 patient lost to follow-up (7.7%). Conclusion: This study describes the clinicopathological characteristics and outcomes of apocrine TNBC. The mean age of 59.5 years and predominance of T1 and N0 tumors and with a majority exhibiting low to moderate proliferation align with prior findings suggesting that apocrine TNBC occurs in older patients with smaller, well-differentiated tumors. The low rates of local recurrence and distant metastasis (7.7% each) and high rate of patients alive without disease (92.3%) support the hypothesis of a more favorable prognosis compared to NST TNBC. Th AR positivity in 84.6% of patients suggests potential for AR therapies, an area warranting further investigation. Limitations include the small sample size and retrospective design, which preclude robust inferential analyses. Future studies with larger cohorts and detailed molecular analyses are needed to confirm these findings and explore treatment response predictors. Citation Format: T. Saruwatari, D. de Albuquerque, V. Primo Basílio, L. Rodrigues Soares, M. De Brot, S. Sanches, V. Cordeiro, E. Santana dos Santos. Clinicopathological Features and Outcomes of Apocrine Triple-Negative Breast Cancer: A Distinct Subtype with Favorable Prognosis abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-10-21.
Saruwatari et al. (Tue,) studied this question.