Immune Checkpoint Inhibitors for Microsatellite Instability High Unresectable Obstructive Colon Cancer: A Report of Two Cases

TL;DR

This paper reports two successful cases where immune checkpoint inhibitors helped treat advanced colon cancer, avoiding traditional surgery and leading to full recovery.

Contribution

The study demonstrates that immune checkpoint inhibitors can safely and effectively treat obstructive MSI-H colon cancer, avoiding decompressive procedures.

Findings

Pembrolizumab monotherapy rapidly improved symptoms and allowed for curative resection in two patients with MSI-H obstructive colon cancer.

Both patients achieved complete or near-complete pathological responses without needing adjuvant chemotherapy.

ICI treatment facilitated oncologically safe R0 resection, avoiding colostomy and other decompressive procedures.

Abstract

Patients with obstructive colon cancer (OCC) with distant metastases often present with a poor general condition, including malnutrition, anemia, and systemic inflammation. Traditionally, these patients undergo stoma creation and/or primary tumor resection followed by systemic chemotherapy. However, for patients with DNA mismatch repair-deficient/microsatellite instability high (dMMR/MSI-H) colorectal cancer, the emergence of immune checkpoint inhibitors (ICIs) has revolutionized treatment strategies, with remarkable antitumor effects. We report two cases of successful management of MSI-H OCC, achieving curative resection while avoiding decompressive procedures, including colostomy creation.

Case 1: A 29-year-old man diagnosed with MSI-H obstructive transverse colon cancer (cT4b stomach, N1b, M1c1) was treated with pembrolizumab monotherapy (200 mg/body, every 3 weeks). The colorectal obstructive scoring system score was 2 at pembrolizumab administration. The patient showed rapid improvement in his abdominal symptoms within 3 days and achieved clinical complete response after eight courses. Laparoscopic partial colectomy with D3 lymph node dissection was subsequently performed safely. He was discharged on postoperative day 8 without postoperative complications. Histopathological analysis confirmed pathological complete response, and the patient was recurrence-free 15 months after surgery without adjuvant chemotherapy. Case 2: A 58-year-old man diagnosed with MSI-H obstructive ascending colon cancer (cT4aN3M1a, LYM) was treated with pembrolizumab monotherapy. The colorectal obstructive scoring system score was 1 at pembrolizumab administration. The patient’s abdominal symptoms improved within 5 days, with marked tumor shrinkage after nine courses. Laparoscopic extended right hemi-colectomy with D3 lymph node dissection was subsequently performed safely, and he was discharged on postoperative day 7 without postoperative complications. Histopathological analysis showed major pathological response (less than 10% viable cancer cells in the resected specimen), with no viable tumor cells in the primary lesion. The patient was recurrence-free 1-year post-surgery, without adjuvant chemotherapy.

This report highlights the potential benefits of ICI treatment for dMMR/MSI-H OCC, particularly for rapid relief of obstruction-related symptoms and facilitating oncologically safe R0 resection. In cases of MSI-H OCC, ICIs can be highly effective as an alternative to traditional decompression procedures.

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