Background: Differential expressions of cancer-associated genes, including histone deacetylases (HDACs), were identified in distinctive molecular subtypes of breast cancer. Compared with hormone receptor-positive breast cancer, triple-negative (TNBC, ER−PR−HER2−) is the most aggressive form of breast cancer. Aims: To determine the association of HDAC7 mRNA expression levels with clinicopathological features and patients' survival with TNBC or ER+PR+HER2− breast cancers. Methods: Total RNA was extracted from 61 TNBC and 74 ER+PR+Her2− tumors. Relative gene expression was evaluated by SYBR Green RT-PCR, normalized to glyceraldehyde-3-phosphate dehydrogenase. The HDAC7 mRNA expression was defined as high or low, according to receiver operating characteristic analysis. Kaplan–Meier and Cox regression analyses for overall survival were assessed to evaluate the prognostic relevance of HDAC7 overexpression. Results: The HDAC7 overexpression was predominantly found in invasive ductal carcinomas (p = 0.023), high histologic grade (p = 0.007), and high nuclear grade tumors (p = 0.030). TNBC subtypes had a significantly lower mean HDAC7 gene expression compared with ER+PR+HER2− tumors (p = 0.005). However, HDAC7 overexpression predicted unfavorable survival of TNBC patients (p = 0.003). Multivariate Cox regression analysis indicated that recurrences (hazard ratio [HR] = 5.432, p = 0.003), and HDAC7 overexpression (HR = 9.287, p = 0.033) persisted as independent prognostic factors for poor survival of TNBC patients. Conclusions:HDAC7 mRNA overexpression is associated with poor survival in patients with TNBC tumors. [ABSTRACT FROM AUTHOR]