Pathological Complete Response in Locally-advanced MSI-H/dMMR Sigmoid Colon Cancer Treated With Pembrolizumab and...

Area of Science:

• Oncology
• Immunotherapy
• Gastroenterology

Background:

• Microsatellite instability-high (MSI-H) and mismatch repair-deficient (dMMR) colorectal cancers respond well to immune checkpoint inhibitors.
• Pembrolizumab offers new treatment avenues for unresectable colorectal cancer.
• Extensive local invasion presents significant surgical and therapeutic challenges.

Purpose of the Study:

• To report a case of locally advanced, extensively invasive MSI-H/dMMR sigmoid colon cancer treated with pembrolizumab and surgery.
• To evaluate the efficacy of pembrolizumab in achieving a pathological complete response in such cases.
• To highlight the potential for curative outcomes through combined modality treatment.

Main Methods:

• A patient with locally advanced sigmoid colon cancer invading the abdominal wall and small intestine was diagnosed with MSI-H/dMMR status.
• Ultrasound-guided biopsy was performed due to endoscopic biopsy challenges.
• The patient received 12 cycles of pembrolizumab followed by sigmoidectomy with en bloc abdominal wall resection and reconstruction.

Main Results:

• Pembrolizumab treatment led to marked tumor regression.
• Histopathological examination after surgery revealed no residual tumor cells in the sigmoid colon or abdominal wall.
• A complete pathological response was achieved, indicating successful treatment.

Conclusions:

• Pembrolizumab combined with aggressive surgical intervention can achieve curative outcomes in extensively invasive MSI-H/dMMR colorectal cancer.
• This approach provides a viable strategy for patients with previously unresectable disease.
• Complete pathological response underscores the effectiveness of neoadjuvant immunotherapy in select colorectal cancer patients.