Case Report: Durable complete response to dual immune checkpoint blockade and EGFR inhibition in microsatellite-stable metastatic duodenal adenocarcinoma
Abstract
BackgroundSmall bowel adenocarcinoma (SBA) is a rare gastrointestinal malignancy with limited treatment options and worse outcomes than colorectal cancer. While immune checkpoint inhibitors (ICIs) show impressive results in mismatch repair–deficient (dMMR)/microsatellite instability–high (MSI-H) tumors, microsatellite-stable (MSS) disease is traditionally considered resistant to immunotherapy.CaseWe describe a man in his 70s with recurrent duodenal adenocarcinoma who experienced disease progression after multiple systemic therapies, including cetuximab plus FOLFIRI. Molecular profiling by liquid biopsy showed MSS status with low tumor mutational burden (TMB = 1 mutation/Mb). Given the lack of standard alternatives, he was treated with nivolumab, ipilimumab, and cetuximab. Tumor regression was observed within 3 months, followed by a complete radiographic response in October 2022 and a complete metabolic response on PET/CT at 12 months. Immune-related adverse events (irAEs) included grade 2 adrenal insufficiency, vitiligo, and pneumonitis, all of which were manageable. At the latest follow-up in April 2026, the patient had maintained a complete response, approximately 42 months after the first documented radiographic complete response and 27 months after discontinuation of all anticancer therapy.ConclusionsThis case describes an exceptional durable complete response to dual immune checkpoint blockade combined with an EGFR inhibitor in MSS duodenal adenocarcinoma. Although the relative contribution of each agent and the presence of pharmacologic synergy cannot be determined from a single case, this observation warrants further investigation in prospective trials with MSS SBA.
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BibTeX
@article{wu2026case,
title = {{Case Report: Durable complete response to dual immune checkpoint blockade and EGFR inhibition in microsatellite-stable metastatic duodenal adenocarcinoma}},
author = {Chia-Ying Wu and Kuan-Chang Lai and Pei-Ying Hsieh and San-Chi Chen},
journal = {Frontiers in Immunology},
year = {2026},
month = nov,
doi = {10.3389/fimmu.2026.1983057},
url = {https://www.frontiersin.org/articles/10.3389/fimmu.2026.1983057},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Case Report: Durable complete response to dual immune checkpoint blockade and EGFR inhibition in microsatellite-stable metastatic duodenal adenocarcinoma
AU - Chia-Ying Wu
AU - Kuan-Chang Lai
AU - Pei-Ying Hsieh
AU - San-Chi Chen
PY - 2026
DA - 2026/11/06
JO - Frontiers in Immunology
DO - 10.3389/fimmu.2026.1983057
UR - https://www.frontiersin.org/articles/10.3389/fimmu.2026.1983057
AB - BackgroundSmall bowel adenocarcinoma (SBA) is a rare gastrointestinal malignancy with limited treatment options and worse outcomes than colorectal cancer. While immune checkpoint inhibitors (ICIs) show impressive results in mismatch repair–deficient (dMMR)/microsatellite instability–high (MSI-H) tumors, microsatellite-stable (MSS) disease is traditionally considered resistant to immunotherapy.CaseWe describe a man in his 70s with recurrent duodenal adenocarcinoma who experienced disease progression after multiple systemic therapies, including cetuximab plus FOLFIRI. Molecular profiling by liquid biopsy showed MSS status with low tumor mutational burden (TMB = 1 mutation/Mb). Given the lack of standard alternatives, he was treated with nivolumab, ipilimumab, and cetuximab. Tumor regression was observed within 3 months, followed by a complete radiographic response in October 2022 and a complete metabolic response on PET/CT at 12 months. Immune-related adverse events (irAEs) included grade 2 adrenal insufficiency, vitiligo, and pneumonitis, all of which were manageable. At the latest follow-up in April 2026, the patient had maintained a complete response, approximately 42 months after the first documented radiographic complete response and 27 months after discontinuation of all anticancer therapy.ConclusionsThis case describes an exceptional durable complete response to dual immune checkpoint blockade combined with an EGFR inhibitor in MSS duodenal adenocarcinoma. Although the relative contribution of each agent and the presence of pharmacologic synergy cannot be determined from a single case, this observation warrants further investigation in prospective trials with MSS SBA.
SN - 1664-3224
ER -