Rectosigmoid-Junction Squamous Cell Carcinoma With pMMR/MSS Achieved a Partial Response Following PD-1 Blockade...

Area of Science:

• Oncology
• Immunotherapy
• Gastroenterology

Background:

• Colorectal squamous cell carcinoma (SCC) is exceptionally rare with a poor prognosis.
• Proficient mismatch repair (pMMR) and microsatellite stable (MSS) colorectal cancers typically show limited response to programmed death ligand-1 (PD-1) blockade monotherapy.
• The efficacy of PD-1 blockade in colorectal SCC remains largely uncharacterized.

Observation:

• A single patient diagnosed with rectosigmoid-junction SCC received combination therapy comprising PD-1 blockade and chemotherapy.
• Computed tomography imaging after 3 months revealed a partial response to the treatment regimen.
• Tumor analysis indicated proficient mismatch repair (pMMR), microsatellite stability (MSS), high PD-L1 expression, and high tumor mutational burden (TMB-High).

Findings:

• The combination of PD-1 blockade and chemotherapy demonstrated potential clinical activity in a patient with pMMR/MSS colorectal SCC.
• High PD-L1 expression and high tumor mutational burden (TMB-High) were observed in the patient's tumor.
• These biomarkers may serve as predictors for treatment response in colorectal SCC patients undergoing PD-1 blockade therapy.

Implications:

• PD-1 blockade combined with chemotherapy could represent a viable therapeutic strategy for colorectal SCC, particularly in patients with pMMR/MSS tumors.
• PD-L1 expression and TMB status may be crucial for patient selection and predicting response to immunotherapy in this rare cancer subtype.
• Further investigation is warranted to validate these findings in a larger cohort of colorectal SCC patients.