Acquired amegakaryocytic thrombocytopaenia after treatment with immune checkpoint inhibitor as part of neoadjuvant treatment in a patient with bilateral breast cancer.

Immune checkpoint inhibitors are a standard treatment for solid metastatic cancer and are now used as neoadjuvant therapy in early triple-negative breast cancer.While haematological immune-related adverse events are known, acquired amegakaryocytic thrombocytopaenia (AAT) is a rare condition characterised by a complete absence of megakaryocytes, leading to severe thrombocytopaenia, with no standardised treatment available.A patient in her early 60s presented with a low platelet count and was initially treated with high-dose methylprednisolone (1 g daily) for suspected immune-mediated thrombocytopaenia, but this was ineffective. A bone marrow biopsy revealed a depletion of megakaryocytes.The treatment was switched to eltrombopag, cyclosporine and tranexamic acid.Despite low platelet levels, the patient successfully underwent bilateral mastectomy with supportive platelet transfusions.Three weeks after starting eltrombopag and cyclosporine, her platelet count returned to normal. AAT in neoadjuvant treatment has not been previously reported, highlighting the need for interdisciplinary collaboration to address these challenges.