Thrombopoietin Receptor Agonists for Thrombocytopenia Secondary to HER2-Targeted Antibody Drug Conjugates

Abstract Trastuzumab emtansine and trastuzumab deruxtecan are widely used in breast cancer and other solid tumor malignancies. Thrombocytopenia is a common adverse event associated with the use of these agents that can lead to a treatment delay, reduction in dose intensity, and discontinuation. The role of thrombopoietin receptor agonists (TPO-RA) remains unknown in this setting. We report a case series of 6 individuals with breast cancer that experienced dose-reductions and therapy delays due to thrombocytopenia secondary to trastuzumab emtansine or trastuzumab deruxtecan therapy and received intervention with TPO-RA. All 6 were able to resume therapy with TPO-RA support. Thrombopoietin receptor agonists (TPO-RA), such as eltrombopag, romiplostim, and avatrombopag, have shown efficacy in treating immune thrombocytopenia; however, their efficacy in improving platelet counts due to HER2-targeted antibody-drug conjugate therapy remains unknown. This article reports a series of cases in which TPO-RA were successfully utilized to treat such thrombocytopenia associated with ado-trastuzumab emtansine(T-DM1) and fam-trastuzumab deruxtecan (T-DXd) therapy.