RESUMO

Trastuzumab emtansine (T-DM1) is a targeted therapy combining trastuzumab and emtansine for human epidermal growth factor receptor 2(HER2)-positive breast cancer, with common side effects including fatigue, nausea, pain, headache, low platelet count, and elevated liver enzymes. Hereditary Hemorrhagic Telangiectasia (HHT) is an autosomal dominant vascular dysplasia characterized by vascular malformations and telangiectasias in various organs. We present a case of a female patient with advanced breast cancer who developed HHT-like symptoms while on T-DM1 treatment. A 59-year-old woman treated with radiotherapy and T-DM1 every 21 days developed recurring nosebleeds and mucocutaneous and liver telangiectasias indistinguishable from HHT three months after receiving the first dose of T-DM1. Other organ vascular malformations were ruled out through screening protocols. The patient had no previous HHT symptoms or family history. Nasal care measures like lubrication and antifibrinolytics (tranexamic acid) were provided. In addition, propranolol was also prescribed due to its antiangiogenic and antitumoral properties, leading to significantly decreased epistaxis and telangiectasias. Microtubule disruptions caused by T-DM1, along with other angiogenic mechanisms may contribute to the development of telangiectasias resembling HHT. The use of propranolol, an initial approach for HHT, proved to be effective in this case. It is crucial for oncologists and HHT specialists to be aware of this rare adverse event associated with T-DM1 and to implement appropriate management strategies.