Immune checkpoint inhibitors (CPIs) are a relatively new class of ‘miracle’ dugs that have revolutionised the treatment and prognosis of some advanced-stage malignancies, and have increased the survival rates significantly. This class of drugs includes cytotoxic T lymphocyte antigen-4 inhibitors such as ipilimumab; programmed cell death protein-1 inhibitors such as nivolumab, pembrolizumab and avelumab; and programmed cell death protein ligand-1 inhibitors such as atezolizumab. These drugs stimulate the immune system by blocking the coinhibitory receptors on the T cells and lead to antitumoural response. However, a flip side of these novel drugs is immune-related adverse events (irAEs), secondary to immune-mediated process due to disrupted self-tolerance. The irAEs in the gastrointestinal (GI) tract/liver may result in diarrhoea, colitis or hepatitis. An accurate diagnosis of CPI-induced colitis and/or hepatitis is essential for optimal patient management. As we anticipate greater use of these drugs in the future given the significant clinical response, pathologists need to be aware of the spectrum of histological findings that may be encountered in GI and/or liver biopsies received from these patients, as well as differentiate them from its histopathological mimics. This present review discusses the clinical features, detailed histopathological features, management and the differential diagnosis of the luminal GI and hepatic irAEs that may be encountered secondary to CPI therapy.

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‘Apoptotic colopathy’ is an umbrella term signifying a pattern of injury where the gastrointestinal biopsy shows a colitic picture with apoptosis as the predominant histological feature. Although the entities within apoptotic colopathy share a common histological feature— ‘apoptosis’, there is a list of varied clinical differential diagnoses that produce this similar histological pattern of injury. These include graft-versus-host disease, drug-induced injury due to multiple drugs (in particular, mycophenolate mofetil, check point inhibitor therapy and some others), infections (particularly cytomegalovirus, adenovirus and some others), immune disorders and other miscellaneous causes. However, the management of these varied differentials is strikingly different, thus necessitating an algorithmic approach for accurate diagnosis and optimal patient management. A definitive diagnosis requires interpretation of varied histological findings in the appropriate clinical context including clinical history, drug history and laboratory findings. This review will focus on the histopathological findings of varied entities that can manifest as ‘apoptotic colopathy’ on assessment of colonic biopsies.

Although most cases showed no pathologic alteration, a minority had significant findings, with the incidence of GISTs higher than that reported in other series. Despite negative preoperative H. pylori testing, 3.2 % were still histologically positive, raising questions about the accuracy of preoperative methods used for H. pylori testing and treatment. Preoperative endoscopy may not be needed in sleeve patients.