Long-term survival in a patient with brain metastases and leptomeningeal disease of breast cancer: a case report of a patient receiving trastuzumab-deruxtecan.

Introduction: The incidence of central nervous system (CNS) metastases in breast cancer (BC) patients is increasing, and the prognosis for those with CNS involvement, especially when accompanied by leptomeningeal disease, remains poor. We present a case of long-term survival in a patient with CNS metastases from HER2-positive BC and discuss the treatment considerations in this context.

Case presentation: A 54-year-old woman with HER2-positive BC developed CNS metastases, including a highly suspicious finding for leptomeningeal disease, 2 years after initial treatment. At the time of her primary BC diagnosis, she received neoadjuvant chemotherapy, followed by breast surgery, adjuvant radiation, and anti-HER2 targeted therapy. Two years later, she developed parenchymal BM, and brain MRI revealed a leptomeningeal involvement, accompanied by neurological symptoms, including an epileptic episode. She underwent surgical resection and stereotactic radiotherapy for the parenchymal BM, followed by reinduction of trastuzumab as systemic treatment. As the disease progressed and neurological symptoms worsened, the patient received T-DM1. After further cerebral progression in 2021, therapy was switched to Trastuzumab-deruxtecan (T-DXd). Since May 2022, she has received 30 cycles of T-DXd (with a reduced dosage of 4.4 mg/kg since August 2023) without evidence of disease progression.

Conclusion: Long-term survival is achievable in patients with CNS metastases from BC, even in the presence of leptomeningeal disease, especially with the use of targeted therapies like T-DXd.