Long-Term Success With a TDM-1 Biosimilar in Recurrent HER2-Positive Breast Cancer With Multisite Metastases: A Comprehensive Case Study

This case report highlights the treatment approaches for breast cancer with metastasis to multiple sites, including the brain, liver, lungs, and bones. It also explores the role of trastuzumab emtansine (T-DM1) and its biosimilar as targeted therapies for HER2-positive breast cancer in long-term treatment. A 54-year-old postmenopausal female patient with recurrent breast cancer and metastasis was treated with trastuzumab and paclitaxel (12 cycles), followed by trastuzumab maintenance therapy (71 cycles). She received radiation therapy of 30 Gy in 10 fractions after presenting with bleeding from the breast lesion. Oral therapy with lapatinib and letrozole was prescribed for a year to treat the breast cancer, along with the lesions and enhanced nodules observed in the patient's lungs, liver, and bones. A year later, she presented with complaints of seizures and loss of consciousness and was diagnosed with brain metastasis. Whole-brain radiation therapy (WBRT) was administered after performing contrast-enhanced computed tomography (CECT). The WBRT was followed by trastuzumab emtansine (T-DM1) biosimilar therapy. Currently, the patient has received more than 30 cycles of T-DM1 and has survived while maintaining a good quality of life. The patient has survived 7.5 years in a stable disease condition after the detection of recurrent breast cancer with metastasis to the liver, lungs, bones, and brain. This case report demonstrates the long-term efficacy of T-DM1 and its satisfactory safety profile. Overall, it provides valuable insights into the management of and challenges faced during the treatment of recurrent breast cancer with metastasis.