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Immunol."],"abstract":"<jats:p>Primary colon squamous cell carcinoma (SCC) is an extremely rare malignancy and associated with a poor prognosis. This case report describes a patient with deficient mismatch repair\/microsatellite instability-high (dMMR\/MSI-H) ascending colon SCC, who was treated at our institution. After receiving four cycles of programmed cell death -1 (PD-1) blockade monotherapy, the tumor exhibited significant regression, and pathological complete response (pCR) was achieved following surgical resection. This case demonstrates that Anti-PD-1 therapy can induce clinically meaningful tumor regression even in this rare colon SCC subtype, suggesting a potential treatment strategy for dMMR\/MSI-H colon SCC. These findings may provide valuable insights for clinicians managing similar cases. However, the feasibility and safety of immunotherapy in dMMR\/MSI-H primary colon SCC require further validation through additional clinical studies.<\/jats:p>","DOI":"10.3389\/fimmu.2026.1688501","type":"journal-article","created":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T06:47:58Z","timestamp":1774421278000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Pathological complete response following immunotherapy in dMMR\/MSI-H ascending colon primary squamous cell carcinoma: a case report"],"prefix":"10.3389","volume":"17","author":[{"given":"Chaoxian","family":"Xiong","sequence":"first","affiliation":[{"name":"Department of Colorectal Surgery, Yunnan Cancer Hospital, The Third Affiliated Hospital of Kunming Medical University","place":["Kunming, China"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Weimin","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of 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