NUMBL (NUMB Like Endocytic Adaptor Protein) is a tumor suppressor protein that plays critical roles in neurogenesis and immune regulation. During embryonic development, NUMBL is required to maintain neural progenitor cells and regulate cell fate decisions, continuing to function postnatally in subventricular zone neurogenesis 1. NUMBL acts as a negative regulator of multiple signaling pathways, including NF-κB signaling through interaction with TAB2, where it impairs TAB2 binding to TRAF6 and inhibits TRAF6 ubiquitination 2. The protein functions primarily through inhibition of Notch signaling pathways, which is essential for proper cell differentiation 3. NUMBL demonstrates tumor suppressive properties across multiple cancer types, with abnormal expression significantly associated with clinicopathologic stages and survival prognosis 4. In melanoma, NUMBL inhibits tumor growth by modulating the immune microenvironment, affecting CD8+ T cells, CD19+ B cells, and NK cells 5. Genetic alterations in NUMBL, including dominant-negative mutations, have been associated with inflammatory disorders such as multisystem inflammatory syndrome in children, where they lead to Notch1 upregulation and regulatory T cell destabilization 6. These findings establish NUMBL as a key regulator of cell fate determination and immune homeostasis.