Clinicopathological features and prognostic factors of apocrine carcinoma of the breast in a cohort of 63 patients

Mammary apocrine carcinoma (AC) is a rare subtype of breast cancer characterized by distinct morphological features. Although generally considered to have a favorable prognosis, the clinicopathological characteristics and prognostic factors of AC remain poorly understood. This single-center retrospective study analyzed 63 patients with AC diagnosed at Asahikawa Medical University Hospital between 2000 and 2024. Clinicopathological features were evaluated, which included tumor size, grade, hormone receptor status, human epidermal growth factor receptor type 2 expression, Ki-67 index, lymphatic and vascular invasion, and patient prognosis. Univariate and multivariate analyses were conducted to identify the independent prognostic factors. The incidence of AC among breast cancer cases was 1.4% (63/4459). All cases diagnosed as AC contained more than 50% apocrine components. Among the invasive ACs, there were 19 cases (34.5%) of pure type AC and 36 cases (65.5%) of non-pure type AC. Univariate analysis showed that a high Ki-67 index (≥ 40%), vascular invasion, and lymphatic invasion were significantly associated with poor prognosis. Multivariate analysis identified Ki-67 index ≥ 40% (HR: 8.096, p = 0.0225) as independent poor prognostic factor. Independent predictor of poor prognosis of AC may include high Ki-67 index. This finding suggests the need for individualized treatment strategies and close postoperative monitoring of high-risk patients.