P566 Colitis due to immunotherapy with anti-PD-1: a case series

De Ruvo, M.(1)*;Barberio, B.(1);Zingone, F.(1);Bonanno, L.(2);Dal Maso, A.(2);Stefano, F.(2);Chiarion Sileni, V.(3);Savarino, E.V.(1);

(1)University of Padua- Division of Gastroenterology, Department Of Surgery- Oncology And Gastroenterology, Padua, Italy;(2)Veneto Institute of Oncology IOV – IRCCS, Oncology 2 Unit- Department of Medical Oncology, Padua, Italy;(3)Veneto Institute of Oncology IOV – IRCCS, Melanoma Unit Department of Oncology, Padua, Italy;


Anti-programmed death-1 (PD-1) drugs have been associated with immune-mediated gastrointestinal adverse events in 0.5-9% of the cases. The aim of this study was to investigate the characteristics of colitis occurring in oncological patients treated with anti-PD-1 drugs.


This is a prospective cohort study including patients referred for new onset colitis at Azienda Ospedaliera of Padua between 2020 and 2022.
All patients were treated with anti-PD-1 drugs at Istituto Oncologico Veneto due to oncological disease [n=2 melanoma, n=1 colorectal cancer, n=1 pleural mesothelioma, n=14 non-small-cell lung cancer (NSCLC)].
Median duration of follow up was 10 months.


Eighteen patients who developed diarrhea (≥G2, CTCAE) following treatment with anti-PD-1 were included (n=12 males, median age 70 years).
The diarrhea began after a mean of seven months of therapy and after two to six months its discontinuation in 3/18 patients.
The mean fecal calprotectin values at diarrhea onset was 1063 ug/g.
Most of the patients (14/18) had their immunotherapy suspended, among them four required hospitalization. All patients were initially treated with systemic steroids (1 mg/kg). Seven patients had ulcerative colitis (UC)-like colitis (n=5 pancolitis, n=2 left colitis) while the others (60%) had microscopic colitis (MC, n=9 collagenous, n=1 lymphocytic) with unspecific inflammatory mucosal abnormalities in half of the cases.
Among patients with UC-like colitis, two were hospitalized and treated with anti-TNFα because of steroid refractoriness; all remaining patients with UC-like colitis are maintaining remission with oral mesalamine or with budesonide non-MMX or low-dose systemic steroid (0.1 mg/kg). Two patients restarted anti-PD-1 drugs with no colitis relapse in the following three months, with mesalamine as maintenance therapy.
Among patients who developed a MC, one required Vedolizumab as maintenance therapy, while 8/10 achieved partial or complete remission with oral budesonide non-MMX or low-dose systemic steroid. Three patients restarted anti-PD-1 drugs with no colitis relapse in the following three months, taking budesonide non-MMX as maintenance therapy.
In our cohort of study all patients with MC were previously treated with anti-PD-1 drugs for NSCLC, while those with UC-like colitis were treated for NSCLC (n=4), melanoma (n=2) and colorectal cancer (n=1).


We observed a significant proportion of microscopic colitis in patients with NSCLC, while UC-like colitis was equally distributed in the other forms of neoplasia.
Men are at higher risk to develop anti-PD-1 induced MC in NSCLC, rather than women.
Anti-PD-1 induced microscopic  colitis presents more frequently endoscopic signs of inflammation.