Which monoclonal antibody is used as first-line therapy along with chemotherapy in metastatic colorectal carcinoma only after confirming absence of KRAS exon 2 mutation?

• A Cetuximab ✓
• B Bevacizumab
• C Panitumumab is excluded but cetuximab is permitted
• D Ramucirumab

Explanation

Cetuximab blocks the ligand-binding domain of EGFR. In tumours with activating KRAS mutations the pathway signals constitutively downstream of EGFR, so receptor blockade gives no benefit; guidelines therefore restrict cetuximab and panitumumab to RAS-wild-type disease. Bevacizumab targets VEGF-B and works regardless of RAS status. Option C is self-contradictory and incorrect: both anti-EGFR antibodies require wild-type RAS.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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