Delayed thrombocytopenia as a rare but serious adverse event secondary to immune checkpoint inhibitor: a case report

Immune checkpoint inhibitors (ICIs) are a recent breakthrough in antitumor drugs, although their overall safety has not been fully defined. Compared to conventional chemotherapy, ICIs exhibit different patterns of immunotoxicity, and immune-related adverse events (irAEs) have an immunological basis that is more toxic than usual and have a broad spectrum of manifestations involving different organ systems. Early recognition of symptoms and timely intervention are very important in managing immune-related adverse events (irAEs). In this study, we report a case of delayed immune thrombocytopenia in a patient treated with nivolumab for small cell lung cancer (SCLC). We found that thrombocytopenia was associated with the presence of platelet antibodies, autoantibodies, and thyroglobulin antibodies, accompanied by a decrease in the number of helper T cells and regulatory T cells. Platelets returned to normal after the removal of antibodies by plasma exchanges and methylprednisolone. We hypothesized that thrombocytopenia in patients was an antibody-driven and T-cell-mediated process. Although these observations indirectly suggest that cytokine changes contribute to immune dysregulation during irAE, prospective validation is needed to explain the confounding etiologies that may contribute to cytokine dysregulation. Therefore, studying the relationship between T cell subpopulations, cytokines and irAE in a larger population may be crucial for identifying biomarkers for ICI.