Mcam stabilizes a luminal progenitor-like breast cancer cell state via Ck2 control and Src/Akt/Stat3 attenuation

Cell state control is crucial for normal tissue development and cancer cell mimicry of stem/progenitor states, contributing to tumor heterogeneity, therapy resistance, and progression. Here, we demonstrate that the cell surface glycoprotein Mcam maintains the tumorigenic luminal progenitor (LP)-like epithelial cell state, leading to Basal-like mammary cancers. In the Py230 mouse mammary carcinoma model, Mcam knockdown (KD) destabilized the LP state by deregulating the Ck2/Stat3 axis, causing a switch to alveolar and basal states, loss of an estrogen-sensing subpopulation, and resistance to tamoxifen—an effect reversed by Ck2 and Stat3 inhibitors. In vivo, Mcam KD blocked generation of Basal-like tumors and Sox10+Krt14+ cells. In human tumors, MCAM loss was largely exclusive of the Basal-like subtype, linked instead to proliferative Luminal subtypes, including often endocrine-resistant Luminal B cancers. This study has implications for developing therapies targeting MCAM, CK2, and STAT3 and their likely effective contexts.