Avatrombopag Optimizes Response to Niraparib by Managing Thrombocytopenia Associated with Poly-ADP Ribose Polymerase (PARP) Inhibition in Ovarian Cancer and Breast Cancer: A Case Series.

BACKGROUND Thrombocytopenia is a potentially treatment-limiting adverse event of particular interest with the PARP inhibitor niraparib. This adverse event may necessitate niraparib dose reduction or treatment discontinuation, resulting in suboptimal treatment outcomes. Here, we report on niraparib dose optimization in 2 patients with breast cancer and 4 patients with ovarian cancer through concurrent administration of the thrombopoietin receptor stimulating agent avatrombopag to mitigate thrombocytopenia, enabling niraparib reescalation and improved clinical response. CASE REPORT Three of 6 patients received niraparib 300 mg daily, the highest recommended dose, for a sustained period. Avatrombopag therapy enabled niraparib dose escalation that led to reductions in biomarkers associated with disease progression. Before initiation of avatrombopag, increases in CA-125 levels, a marker for ovarian cancer, were observed in association with niraparib dose interruption, and in 2 patients with ovarian cancer CA-125 levels fell in response to niraparib dose escalation enabled by concurrent avatrombopag therapy. Further, in 2 patients with metastatic breast cancer, intracranial response was observed in association with avatrombopag-enabled niraparib therapy. In 1 patient with metastatic breast cancer, niraparib induced an intracranial response, while previous use of talazoparib had not, confirming preclinical findings of superior blood-brain-barrier penetrance with niraparib. CONCLUSIONS Avatrombopag is currently approved for use in chronic immune thrombocytopenia and thrombocytopenia associated with chronic liver disease in patients undergoing a surgical procedure. A clinical trial of avatrombopag for chemotherapy-induced thrombocytopenia is ongoing. Preliminary results in these 6 patient cases demonstrate the need for a confirmatory trial of avatrombopag for optimizing the dose of niraparib.