Cereblon (CRBN) is a substrate receptor of the Cullin-4 RING E3 ubiquitin ligase complex (CRL4CRBN) that plays a pivotal role in targeted protein degradation . Originally associated with autosomal recessive non-syndromic mental retardation, CRBN gained clinical prominence as the primary molecular target of thalidomide and its immunomodulatory drugs (IMiDs) derivatives, lenalidomide and pomalidomide . Upon IMiD binding, CRBN undergoes a neomorphic functional shift, recruiting lymphoid transcription factors IKZF1 (Ikaros) and IKZF3 (Aiolos) for ubiquitination and proteasomal degradation, thereby exerting anti-myeloma effects and modulating immune responses . CRBN mutations, including point mutations and splice variants, occur in 12-30% of IMiD-refractory multiple myeloma patients and represent a key mechanism of acquired drug resistance . Beyond hematologic malignancies, CRBN has emerged as a versatile platform for proteolysis-targeting chimeras (PROTACs), enabling targeted degradation of oncogenic proteins in both hematologic and solid tumors . Recent structural and functional studies classify CRBN mutations into loss-of-function, neutral, and agent-dependent categories, guiding therapeutic strategies including next-generation CELMoD agents .