OBJECTIVE Cytokeratins (CK) 5/6 and 17, myoepithelial markers, are also expressed in a proportion of breast carcinomas. Breast carcinomas expressing basal epithelium cytokeratins constitute a tumor subgroup that shows common but heterogeneous morphological, genetical, and immunophenotypical features and is associated with poor clinical outcome. The aim of this study was to determine the incidence of basal expression of cytokines CK5/6 and CK17 in the tested samples of ductal invasive breast cancers, as well as to test the presence of a correlation of tumor expression of basal cytokines and clinicopathological prognostic factors: age, the level of histological differentiation, hormone receptor status, HER2 (human epidermal growth factor receptor 2) protein expresion and HER2 gene amplification in tumorous tissue. METHODS Immunohistochemistry (IHC) was used to evaluate the CK5/6 and CK17 status of 121 ductal invasive breast cancers. The results thus obtained were compared with clinicopathological characteristics. RESULTS From the 117 analyzed tumor specimens, 22% and 30% were immunohistochemically positive for CK5/6 and CK17, respectively. Basal cytokeratins showed significant inverse relationship with estrogen and progesterone receptor status and HER2 protein expression. CK5/6 and CK17 immunoreactivities were directly associated with triple-negative phenotype and higher histological grade. CONCLUSIONS Our findings are similar to reports that tumours expression of basal cytokeratins are correlated with adverse pathological parameters. Given the limited number of emerging therapeutic targets in these tumors, routine IHC identification of basal-like subtype as a poor prognostic group of breast cancer could be based on the expression of basal CKs.