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BACKGROUND Ado-trastuzumab emtansine (T-DM1) is indicated for use in both early-stage and metastatic breast cancer. This antibody-drug conjugate uses a toxic payload, emtansine, which is delivered directly to the malignant cells via the covalently linked trastuzumab antibody. Emtansine is a microtubule inhibitor and this targeted therapy is used to decrease adverse events. While the package insert acknowledges that it is an irritant with infusion site extravasation injury as a known adverse event, it does not give clear guidance on extravasation treatment. This case report describes the case of a 38-year-old woman with breast cancer being treated with T-DM1 who experienced extravasation and soft-tissue injury, and the medical management she received. CASE REPORT A 38-year-old woman with no previous medical history was diagnosed with hormone receptor-negative and human epidermal growth receptor 2 breast cancer. After refusing port placement, she was treated with T-DM1 via peripheral intravenous injection. She experienced infiltration of T-DM1 and developed widespread erythema, blistering, and pain. She was treated with a topical steroid (clobetasol), topical calcineurin inhibitor (tacrolimus), oral antibiotic (cefadroxil), high-dose vitamin D (ergocalciferol), and pain management (gabapentin) with almost complete resolution in 4 weeks. CONCLUSIONS This case report describes a T-DM1 skin extravasation treated with multimodal medical measures as opposed to a more conservative approach. We reaffirm that the use of port access when administering T-DM1 is critical to prevent extravasation, and we recommend multimodal management, including antibiotics and topical therapies, to prevent infection and expedite wound healing if extravasation occurs.