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Colorectal Cancer — SCE Medical Oncology MCQ

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HardGI CancersColorectal CancerSCE Medical Oncology

A 55-year-old woman with metastatic colorectal cancer undergoes extended RAS testing (KRAS and NRAS exons 2, 3, 4). Why is extended RAS testing critical before prescribing anti-EGFR therapy?

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Correct answer: C — Exclude activating KRAS and NRAS variants before anti-EGFR therapy

Cetuximab or panitumumab benefit requires absence of activating KRAS and NRAS variants across the extended RAS exons. Exclude KRAS exon-two variants before selecting anti-EGFR therapy: KRAS exon-two testing misses other resistance-mediating KRAS and NRAS variants. Exclude BRAF-V600E variants before selecting anti-EGFR therapy: BRAF status adds prognostic and treatment information but cannot substitute for all-RAS testing. Exclude PIK3CA exon-twenty variants before selecting anti-EGFR therapy: PIK3CA testing is not the required gatekeeping biomarker. Exclude HER2 amplification before selecting anti-EGFR therapy: HER2 may inform resistance or later targeting, but all-RAS status remains essential.

Reference: NICE NG151 colorectal cancer: recommendations (Current NICE recommendations, accessed July 2026): https://www.nice.org.uk/guidance/ng151/chapter/Recommendations