Fatal Immune Response Associated with Anti-PD1: Pathological Insight

The recent introduction of immune checkpoint inhibitor therapy with anti- PD-1 agents has shown encouraging responses in gastrointestinal oncology. However, it is also known to possibly result in uncontrolled T cell autoreactivity, leading to a broad range of immune related adverse events. We present a patient who developed sequential immune-related hematologic and hepatic complications following pembrolizumab therapy for metastatic colon cancer. In particular, we describe in detail the histopathologic and immunohistochemical findings in the liver and bone marrow, adding to the spectrum of morphological changes which may be observed in association with PD-1 inhibitor therapy. The report also highlights the occurrence of these adverse reactions even after discontinuation of immunotherapy, eventually resulting in the death of the patient.