Background: CK5 positive cells represent progenitors for glandular and myoepithelial lineages of mammary epithelium. During epithelial differentiation there is a gradual decrease of CK5 expression. In case of benign lesions the proliferating luminal cells show a high expression of CK5. Contrary, the majority of malignancies which are derived from differentiated glandular cells line do not reveal immunohistochemical staining with CK5 marker. The aim of this study was to compare the expression of basal cytokeratin CK5 vs hormone receptors, HER2, Ki67 and molecular subtype’s immunohistochemically defined in the primary breast carcinomas of NST type. Material and methods: We processed 108 invasive breast carcinomas of NST type. The specimens were formalin-fixed and paraffin-embedded as traditionally. Sections were immunostained (ER, PR, HER2, CK5 and Ki67) automatically with Leica Bond-Max autostainer. Results: Breast carcinoma of NST type was in majority of cases CK5 negative (94 cases/87%). The positive CK5 cases had a high grade of differentiation. CK5 negative tumors were usually hormone positive, but in 8 cases/6.5% a combined simultaneous CK5-ER (PR) positive expression was determined. From 22 HER2 positive cases, 16 were CK5 negative. CK5 value correlated statistically significant with all used markers, except grade of differentiation: a positive Pearson coefficient was determined in relation to HER2 and Ki67, and a negative one compared to hormone receptors and molecular subtype. Conclusions: We support CK5 potential value in molecular subtype’s differentiation. Breast carcinoma of NST type is usually CK5 negative and hormone positive. The presence of cases with simultaneous expression of CK5 and hormone receptors is an open field to debate the existence of other, transient molecular subtypes and we expect a further confirmation in larger study groups.