Rituximab is used in CD20-positive B cell non-Hodgkin lymphoma. Its antitumour effect is mediated primarily by which mechanisms?

• A Complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity ✓
• B Inhibition of thymidylate synthase after intracellular conversion
• C Blocking of the IL-6 receptor on malignant B cells
• D Irreversible inhibition of the proteasome in plasma cells

Explanation

Rituximab is a chimeric IgG1 monoclonal antibody against CD20 expressed on pre-A and mature A cells but not stem cells or plasma cells. It kills target cells mainly through complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity, with a contribution from direct induction of apoptosis. The best distractor, option D, describes bortezomib, which targets plasma cells that lack CD20, so rituximab cannot act there.

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

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Written and medically reviewed by the StethoPrep medical team.