In the present study, we investigated the relationship between CD90 expression and breast cancer malignacy by two different and complementary approaches: a) assessment of CD90 protein expression in human patient samples using a breast cancer Tissue Microarray (TMA) Array upon ten years of patient follow-up; b) investigation of the functional role of CD90 in basal-like breast cell lines by both gain of function studies, using CD90 ectopic expression in the non-tumorigenic MCF10A cell line and loss of function, in the highly malignant Hs578T triple-negative breast cancer cell line. Here, THY1 is linked to breast cancer.