A Case of Immune Thrombocytopenia as a Rare Side Effect of an Immunotherapy with PD1-Blocking Agents for Metastatic Melanoma.

Background Checkpoint blocking agents such as pembrolizumab or nivolumab may induce a diversity of mostly autoimmune-mediated side effects. These autoimmune phenomena mainly affect ductless glands such as the pituitary gland (hypophysitis), the thyroid gland (thyreoiditis), the skin (vitiligo and rash), the colon (colitis), and the lung (pneumonitis). Furthermore, many other organs or organ systems may be affected. Case Report This work describes a case of an immune thrombocytopenia that developed or rather became clinically significant shortly after initiation of a systemic therapy with first nivolumab and later pembrolizumab given due to metastatic melanoma. Platelet counts before this systemic therapy were slightly decreased with values around 110/nl (normal value 140-400/nl). Thrombocytopenia developed or became apparent rapidly within 10 days after the first intravenous application of nivolumab and worsened after changeover to pembrolizumab. Therapy had to be stopped due to disease progression and steady aggravation of thrombocytopenia. Immune hematology assays could prove an autoimmune mediated genesis of thrombocytopenia. Conclusion Checkpoint inhibitors may induce a multiplicity of mostly autoimmune-mediated side effects. In contrast to chemotherapy-induced cytopenia that results from bone marrow toxicity, thrombocytopenia in melanoma patients treated with checkpoint inhibiting substances seems to result from autoimmune-mediated side effects in the majority of the cases. Thorough laboratory controls during these therapies are therefore required. In case of thrombocytopenia, immune hematology testing to diagnose or rule out immune thrombocytopenia is indispensable.