Prognosis in triple‐negative apocrine carcinomas of the breast: A population‐based study

BACKGROUND: Triple‐negative apocrine carcinoma (TNAC) of the breast is a very rare type of breast cancer. Furthermore, the clinicopathological features, prognosis, and potential impact of treatment strategies in TNAC remain unclear. METHODS: Data from the Surveillance, Epidemiology, and End Results (SEER) program were used to identify breast cancer patients diagnosed between 2010 and 2016 with TNAC and triple‐negative breast cancer (TNBC, IDC [invasive ductal carcinoma], NOS [not otherwise specified]). Chi‐squared tests were used to examine the categorical variables between the two groups. Overall survival (OS) of TNAC and TNBC was assessed by Kaplan‐Meier analyses and Cox regression. Breast cancer‐specific survival (BCSS) was evaluated by Nelson‐Aalen analyses and competing risk regression. RESULTS: We identified 31 362 patients from the SEER database, including 366 patients with TNAC and 30 996 patients with TNBC. TNAC was correlated with older age, lower T stage and lower tumor grade. Patients with TNAC had better OS compared with TNBC patients; the 5‐year OS rates were 82.2% vs 73.5% (P < .001). The breast cancer‐related death rate was significantly lower in patients with TNAC than in patients with TNBC, with a 5‐year cumulative incidence of 9.1% vs 22.9% (P < .001). Chemotherapy was significantly associated with improved OS in TNAC patients, but radiotherapy was not associated with OS in TNAC patients. In the multivariable Cox regression, TNAC was still associated with improved OS (HR [hazard ratio], 0.61; 95% CI [confidence interval] 0.45‐0.83; P = .002). In the multivariable competing risk regression, the significantly higher BCSS in patients with TNAC compared patients with TNBC remained (subdistribution HR [SHR], 0.42; 95% CI, 0.27‐0.64; P < .001). CONCLUSION: Patients with TNAC had a better prognosis than patients with TNBC, and chemotherapy was associated with survival advantages in TNAC patients.