Extramedullary Multiple Myeloma.

Extramedullary disease (EMD) of multiple myeloma (MM) is a critical indicator of disease progression, with a complex pathophysiology involving tumor microenvironment dysregulation, chromosomal abnormalities, and aberrant signaling pathway activation. Advances in detection technologies have significantly improved EMD diagnosis rates in recent years, but clinical treatment still faces challenges such as high drug resistance rates and difficulties in managing lesions at specific sites. This article systematically reviews the definition, classification, biological characteristics, pathophysiological mechanisms, diagnostic methods, current treatment strategies, and emerging therapeutic challenges of EMD. It emphasizes the interactions between different pathogenic factors and the heterogeneous therapeutic responses of various EMD subtypes, aiming to provide a comprehensive reference for clinical practice and research directions.