Updated publication reference for PubMed record(s): 31644363, 33146709. The MCF7 cell line represents a typical epithelial cell line and corresponds to luminal A breast cancer (estrogen-responsive). Overexpression of HAX1 was demonstrated in MCF7 cell line as well as in breast cancer samples, suggesting a role of HAX1 in breast cancer progression. HAX1 is a 32-kDa protein of unknown structure, involved in the regulation of apoptosis, cell migration and calcium homeostasis. It was also shown to bind mRNA. Scarcity of structural elements and the presence of a disordered region, inferred from HAX1 sequence, suggests that HAX1 is intrinsically disordered, and may have many protein-protein interactions. So far about 40 different proteins were characterized as HAX1 protein partners. In the present work, applying immunoaffinity chromatography coupled with mass spectrometry, we identified new candidates for HAX1 binding partners in breast cancer cells. Newly identified proteins may be divided into three, partially overlapping groups: cytoskeleton-associated proteins, GTP-ase associated proteins and RNA-binding proteins. These results imply that HAX1 has more protein partners than hitherto described. Subsequent analysis of these interactions may shed some light into molecular mechanisms of HAX1 functions.