A 72-year-old woman undergoes right hemicolectomy for stage IIIB (T3N2a) colon cancer. Microsatellite instability (MSI) testing on the surgical specimen reveals high-level MSI (MSI-H). Which adjuvant chemotherapy decision is most directly influenced by this finding?

• A MSI-H status mandates FOLFOX (oxaliplatin + leucovorin + 5-FU) for 6 months
• B MSI-H stage III colon cancer should receive adjuvant capecitabine monotherapy only
• C MSI-H status is a contraindication to any adjuvant chemotherapy and only surveillance is recommended
• D MSI-H status in stage II predicts no benefit from fluoropyrimidine monotherapy adjuvant chemotherapy; however, stage III MSI-H still benefits from FOLFOX ✓

Explanation

MSI-H (dMMR) colon cancer has distinct prognostic and predictive implications. In stage II disease, dMMR/MSI-H is a good prognostic marker and predicts lack of benefit from 5-FU monotherapy adjuvant chemotherapy (QUASAR, ASCO evidence-based guidelines). However, in stage III (node-positive) disease, including MSI-H, adjuvant oxaliplatin-based combination chemotherapy (FOLFOX) still provides meaningful survival benefit — this is a key distinction tested in examinations. MSI-H stage III patients should not be denied oxaliplatin-based adjuvant therapy.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.