MUC4 and neoplasm: Significantly, the above analysis and the novel finding that MUC4/Y triggers positive feedback loops related to malignant activity not only suggest that tumor cells can engage MUC4/Y to express survival factors concomitantly to resist adverse conditions in the microenvironment, e.g., in the circulatory systems during metastasis, but also suggest that tumor cells can exploit MUC4/Y expression to affect the tumor milieu by increasing the expression of cytokines, growth factors, and adhesion molecules, although the lack of the TR domain mainly relates to cell–ECM and cell–cell interplay [40,41].