Triple-negative apocrine carcinoma: A rare pathologic subtype with a better prognosis than other triple-negative breast cancers.

BACKGROUND AND METHODS Apocrine adenocarcinoma is a rare subtype of breast cancer. We sought to compare the characteristics and survival of patients diagnosed with triple-negative apocrine adenocarcinoma to those of patients diagnosed with triple-negative invasive ductal carcinoma. Utilizing data from the National Cancer Database between 2004 and 2013, 70 524 eligible female patients with triple-negative breast cancer were identified including 566 patients with apocrine adenocarcinomas and 69 958 patients with invasive ductal carcinoma. Descriptive statistics for each variable were reported. A comparison of each covariate between the study cohorts was assessed in univariate and multivariate analysis. Cox proportional models were used to calculate hazard ratios. Additionally, the propensity score matching method was implemented to reduce treatment selection bias. RESULTS Patients with triple-negative apocrine tumors were more likely to be older, Caucasian, and have smaller, moderately to well-differentiated tumors. Multivariable analysis noted a significantly improved survival for patients with triple-negative apocrine carcinoma (TNAC) vs triple-negative invasive ductal carcinoma (TNBC) (hazard ratio [HR] 0.65 [95% confidence interval [CI] [0.53-0.81], P = 0 < .001). Propensity score matching analysis confirmed a significant difference in overall survival for patients with TNAC in comparison to TNBC (HR 0.79 [95% CI [0.63-1.00], P = .05). DISCUSSION Triple-negative apocrine adenocarcinomas have a modestly improved long-term survival when compared with triple-negative invasive ductal cancers.