CMTM1 (CKLF-like MARVEL transmembrane domain containing 1) is a membrane-associated protein with multiple alternatively spliced isoforms that functions as a regulator of cell proliferation, apoptosis, and immune cell activity. The protein contains a MARVEL domain capable of activating and directing immune cell chemotaxis 1. CMTM1 operates through calcium signaling mechanisms; specifically, the CMTM1-v5 isoform interacts with CAML (calcium-modulating cyclophilin ligand) to negatively regulate endoplasmic reticulum Ca2+ responses, triggering caspase activation and mitochondrial cytochrome c release 2. CMTM1 demonstrates context-dependent oncogenic roles across multiple cancer types. In lymphoma, CMTM1-v5 overexpression induces apoptosis in vitro and extends survival in xenograft models 2. Conversely, in glioblastoma, CMTM1 promotes tumor cell invasion and proliferation, with elevated expression correlating with shorter overall survival 3. In breast cancer, the CMTM1_v17 isoform enhances proliferation and confers TNF-α-induced apoptosis resistance 4, while in non-small cell lung cancer, CMTM1_v17 associates with chemotherapy resistance and poor prognosis following neoadjuvant chemotherapy 5. Recent evidence indicates CMTM1 expression correlates with M2 macrophage and regulatory T cell infiltration in esophageal carcinoma 6, suggesting immunomodulatory functions. These findings position CMTM1 isoforms as potential diagnostic biomarkers and therapeutic targets in multiple malignancies.