Metastatic urothelial bladder carcinoma is an incurable disease. For years, the therapeutic options were limited to platinum based chemotherapy with modest efficacy. Considering the large mutational burden in bladder cancer, immunotherapy became a standard of care in the second line and in the front line when patients are unfit for platinum based regimen. Thus, oncologists are dealing with new side effects and toxicities.

We report the case of a 66-year-old male patient, smoker, diagnosed with urothelial bladder cancer, with initial metastases to the lungs, retroperitoneal and mediastinal lymphadenopathies. He received a first-line chemotherapy consisting of cisplatin and gemcitabine. After 3 cycles, the evaluation showed a partial response. The response was maintained after 6 cycles and a decision of therapeutic pause was taken. Three months later, the follow-up imaging revealed pulmonary and nodal progression. Immunotherapy was initiated with a checkpoint inhibitor. Partial response was obtained after 3 cycles with good clinical and biological tolerance. After the fourth cycle, he developed an isolated grade I thrombocytopenia that worsened to grade III, before the administration of the sixth cycle. CT-scan confirmed the persistence of partial response. Immunotherapy was put on hold. A bone scan excluded bone metastases. Bone marrow aspirate and biopsy were in favor of a peripheral origin of thrombocytopenia without any dysplasia or infiltration by metastatic cells. After completing the viral and autoimmune work-up, the diagnosis of autoimmunethrombocytopenia secondary to immunotherapy was made. The patient received the same regimen administered for idiopathic thrombocytopenic purpura based on dexamethasone 40 mg daily for 4 days. Platelet count began to recover with normalization after one week. Immunotherapy was discontinued. Six months later, the disease progressed with interval appearance of new liver metastases. A third line chemotherapy was administered without any response. The patient’s clinical condition deteriorated and he died as a result of progression of the metastatic disease. Autoimmune thrombocytopenia has been rarely reported as an autoimmune disorder related to immunotherapy. Clinicians must exclude all other causes of thrombocytopenia before validating this diagnosis. Its management is extrapolated from that of idiopathic thrombocytopenic purpura.