At a mechanistic level, not all of the signaling pathways modified by exercise-conditioned serum involved in the process of inhibition of tumor proliferation are yet known; however, the results suggest a possible modulation of specific myokines (i.e., IL-6, IL-15, and oncostatin M [OSM]) and the Hippo tumor suppressor pathway in both cell lines, with a partial increase in YAP phosphorylation, and, only in breast cancer cells, the possible involvement of the Wnt/ß-catenin pathway, credited with a significant decrease in GSK3ß phosphorylation (Figure 1). This evidence concerns the gene OSM and breast cancer.