Case Report: Medullary carcinoma of the pancreas with MLH1 promoter hypermethylation, induced deficient mismatch repair, successfully treated with an immune checkpoint inhibitor

Case Report: Medullary carcinoma of the pancreas with MLH1 promoter hypermethylation, induced deficient mismatch repair, successfully treated with an immune checkpoint inhibitor

We report the case of a 75-year-old woman with a pancreatic body mass. Pathological findings from endoscopic ultrasonography-guided fine-needle aspiration revealed medullary carcinoma of the pancreas (MCP). Deficient mismatch repair (dMMR) and high microsatellite instability (MSI-H) were identified...

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Main Authors: Koushiro Ohtsubo, Shigeki Sato, Hiroyuki Sakaguchi, Hiroshi Kotani, Akihiro Nishiyama, Kaname Yamashita, Seiji Yano, Fumihito Toshima, Dai Inoue, Toshifumi Gabata, Hiroko Ikeda, Atsushi Watanabe, Kenji Notohara, Takao Fujisawa, Yoshiaki Nakamura, Takayuki Yoshino, Kunio Miyake, Kazuhiro Miwa, Shinji Takeuchi
Format: Article
Language:English
Published: Frontiers Media S.A. 2025-03-01
Series:Frontiers in Oncology
Subjects:
medullary carcinoma of the pancreas
deficient mismatch repair
microsatellite instability
MLH1 hypermethylation
immune checkpoint inhibitor
pembrolizumab
Online Access:https://www.frontiersin.org/articles/10.3389/fonc.2025.1551038/full
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Summary:We report the case of a 75-year-old woman with a pancreatic body mass. Pathological findings from endoscopic ultrasonography-guided fine-needle aspiration revealed medullary carcinoma of the pancreas (MCP). Deficient mismatch repair (dMMR) and high microsatellite instability (MSI-H) were identified through immunohistochemistry and next generation sequencing, respectively. While immunohistochemistry suggested MLH1 abnormality, no MLH1 mutation was; hypermethylation of the MLH1 promoter was later confirmed via bisulfite sequencing. The patient initially received nab-paclitaxel plus gemcitabine, achieving tumor shrinkage. Upon tumor regrowth, she was treated with the anti-programmed cell death-1 immune checkpoint inhibitor (ICI) pembrolizumab, which resulted in significant tumor reduction. This is the first case report of MCP with dMMR/MSI-H due to MLH1 promoter hypermethylation, effectively treated with an ICI.
ISSN:2234-943X

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