Year: 2026
Type: article
Study design: Case Report
Abstract: Background: Gastric mucinous adenocarcinoma (GMA) and appendiceal mucinous adenocarcinoma (AMA) are rare neoplasms that frequently present at advanced stages characterized by peritoneal dissemination. The simultaneous occurrence of these two malignancies is exceedingly uncommon. Case presentation: A 66-year-old man presented with abdominal discomfort and was initially diagnosed with gastric adenocarcinoma based on endoscopic biopsy findings. Computed tomography imaging revealed the presence of ascites and peritoneal nodules. Following neoadjuvant chemoimmunotherapy comprising XELOX and sintilimab, diagnostic laparoscopy identified a concurrent AMA accompanied by pseudomyxoma peritonei (PMP). Subsequently, the patient underwent radical gastrectomy, appendectomy, and hyperthermic intraperitoneal chemotherapy (HIPEC). Histopathological examination confirmed the synchronous presence of GMA and AMA. Importantly, serial molecular analyses demonstrated a treatment-induced transition from mismatch repair-deficient (dMMR)/microsatellite instability-high (MSI-H) status to mismatch repair-proficient (pMMR) status. Conclusion: This rare case highlights the critical importance of comprehensive preoperative imaging and meticulous surgical evaluation in the diagnosis of uncommon synchronous malignancies. Furthermore, the observed alteration in molecular phenotype following chemoimmunotherapy suggests that such treatment modalities may influence tumor biology.
Source: Frontiers in Oncology
Authors: Guangchao Liu, Cheng Jiao, Sen Wang, Shuai Qi, Cuisha Zhang, Qiufang Xing, Wei Liu
Institution: Bethune International Peace Hospital
Language: English
Subfield: Surgery
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $3,801
OpenAlex ID: W7154447173