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Remarkable and Durable Tumor Response to Pembrolizumab in Locally Advanced dMMR/MSI-H Rectal Cancer
Ayumu Hosokawa1, Rin Yamada2, Yukiko Otsuki3
1Department of Clinical Oncology, University of Miyazaki Hospital, Miyazaki, Japan; ayhosoka@med.miyazaki-u.ac.jp.
Background/Aim:
Immune checkpoint inhibitors have demonstrated significant clinical efficacy in patients with mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) colorectal cancer. Although current evidence is based on studies with limited sample sizes, recent findings suggest that anti-programmed cell death-1 (PD-1) antibodies are highly effective in patients with locally advanced dMMR/MSI-H rectal cancer.
Case Report:
We report the case of a 70-year-old man with locally advanced MSI-H rectal cancer who exhibited a remarkable and durable response to pembrolizumab. Histopathological examination revealed the infiltration of CD8-positive T lymphocytes and clusters of PD-L1-expressing macrophages within the tumor tissue. CD103-positive tissue-resident memory T-cells have also been identified in the tumor microenvironment, suggesting a robust and sustained local immune response.
Conclusion:
Immune checkpoint blockade may represent a promising nonsurgical treatment option for patients with locally advanced dMMR/MSI-H rectal cancer.
