On bone marrow biopsy, a patient with multiple myeloma shows plasma cells that are CD38+/CD138+/CD56+/CD19-/CD45-. CD56 expression in myeloma plasma cells (absent on normal plasma cells) is clinically significant because it:

• A Mediates resistance to bortezomib via inhibition of proteasomal degradation
• B Is the therapeutic target of daratumumab
• C Activates NK cell-mediated lysis, improving immune surveillance
• D Confers ability to form bone marrow niches via VLA-4/VCAM-1 interactions, reducing circulating plasma cells ✓

Explanation

CD56 (NCAM, neural cell adhesion molecule) is aberrantly expressed on myeloma plasma cells (normally absent on polyclonal plasma cells). CD56 promotes adhesion to bone marrow stroma, allowing malignant plasma cells to remain sequestered in the marrow rather than circulating. This reduces leukemic spillage. In plasma cell leukaemia (a more aggressive variant), CD56 is frequently absent, correlating with high circulating plasma cell burden. Daratumumab targets CD38, not CD56. Bortezomib resistance is mediated by proteasome subunit mutations, not CD56.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.