Histotripsy for multifocal breast cancer liver metastases with early complete metabolic response: a case report.

Histotripsy is a non-thermal, non-ionizing focused ultrasound therapy that mechanically disrupts tissue through acoustic cavitation. We present a case of a woman with estrogen receptor-positive metastatic breast cancer who developed progressive multifocal liver metastases despite having failed multiple lines of systemic therapies. She underwent two histotripsy treatments staged approximately six weeks apart, using a lobar approach to sequentially treat left- and right-lobe lesions, targeting a total of 10 hepatic lesions. She tolerated both procedures well without any complications or interruption of her targeted therapy (trastuzumab deruxtecan). Follow-up PET/CT performed two months after the second treatment demonstrated complete metabolic response in the liver and overall disease regression, which was again observed on a subsequent PET/CT performed six months later. Follow-up MR imaging four and seven months after the second histotripsy revealed expected post-treatment involution of the treatment zones. This case highlights the ability of histotripsy to treat patients with advanced liver metastases in a staged fashion to minimize potential toxicities. These encouraging early results support the need for more data to confirm the role of histotripsy in advanced metastatic breast cancer patients who have limited treatment options.