Immune-Mediated Thrombocytopenia Induced by Niraparib: A Clinically Relevant Case.

Immune-mediated thrombocytopenia secondary to niraparib is very rare; pharmacovigilance signals are scarce, and the true incidence is unknown. We report a 64-year-old woman, negative for BRCA pathogenic variants, with stage IIIC high-grade serous carcinoma of the ovary, fallopian tube and peritoneum, who started maintenance niraparib 300 mg/day after neoadjuvant chemotherapy and cytoreduction surgery. Platelets fell to grade 1 in week 1 and grade 2 in week 2, leading to interruption. One week later, she presented with grade 4 thrombocytopenia (2×10^3/µL) and petechiae. There was no anaemia or other cytopenias; smear showed no schistocytes; coagulation, direct antiglobulin test and viral serologies were negative. Dexamethasone 40 mg/day for four days restored counts. Re-challenge at 200 mg/day reproduced grade 2 thrombocytopenia by week 2 and again resolved with steroids; niraparib was permanently discontinued. One year post-surgery, she remains without recurrent thrombocytopenia or disease progression. This pattern supports an immune mechanism and underscores the need for steroid therapy and withdrawal.