[Clinicopathological characteristics of anti-PD-1 associated gastroenteritis]

Objective: To investigate the clinicopathological features of anti-PD-1 related gastroenteritis, understand and recognize the disease, and avoid misdiagnoses. Methods: Three cases of anti-PD-1 related gastroenteritis diagnosed and treated at the Zhongshan Hospital Affiliated to Fudan University, Shanghai, China from 2020 to 2021 were collected. The clinical and pathological features were analyzed and the patients were followed up by telephone. Results: The three patients were all male and aged 63, 39 and 73 years, respectively. They had previously developed gastrointestinal symptoms as a result of immunotherapy for a malignant tumor. Endoscopically, 2 patients presented with pancolitis, and 1 patient presented with a large antral ulcer involving the pyloric canal in the stomach. Histologically, there were marked atrophy and thinning of the epithelium, diffuse infiltration of numerous neutrophils in the lamina propria, formation of micro-abscesses in the crypt/glandular lumen, structural changes (branching and distortion) of the glands, and significant glandular dilatation. In addition, chronic inflammatory features (e.g., lymphoplasmacytosis) were focally seen in 2 cases. Cytomegalovirus immunohistochemical stains were negative in all 3 cases. Based on the history and morphology, all 3 cases were diagnosed as anti-PD-1 related gastroenteritis. According to the above diagnosis, the treatment for all 3 patients was to stop anti-PD-1 therapy and use corticosteroids. Clinical follow-up was conducted. The gastrointestinal symptoms of all 3 patients improved significantly and diarrhea symptoms were relieved after stopping immunotherapy. Conclusions: Anti-PD-1 related gastroenteritis is not rare, but pathologists may lack sufficient understanding of it. Combined with clinical history and pathologic characteristics of the lesion, pathologists should consider this disease to avoid the misdiagnoses and missed diagnoses.