Histotripsy of Liver Metastases: Short-Term Safety and Imaging Findings

Histotripsy is a non-invasive ultrasound-based tumor ablation modality. This study aims to describe the preliminary safety and short-term imaging findings related to histotripsy of liver metastases.

All patients who underwent histotripsy for liver metastases from February 2024 to January 2025 at a single center were retrospectively reviewed. Demographic, clinical, imaging, procedural, and adverse event data were collected via chart review. Immediate post-treatment ablation zones were measured on CT and compared to pretreatment tumor size and treatment cavity size on follow-up imaging. Untreated tumors were assessed using revised RECIST criteria to evaluate for off-target effects.

Histotripsy was performed on 56 metastatic liver tumors (most common: 32% colorectal, 18% breast) in 26 patients (54% female, age 59.1 ± 15.6y). All patients were discharged within 36 h. Immediate post-procedural ablation zones (36.6 + 13.1 mm) were larger compared to pretreatment tumors (30.5 + 18.5 mm) (p = 0.0013). One-month ablation zones (31.5 + 16.7 mm) were smaller compared to immediate post-procedural ablation zones (p = 0.00064). Two patients experienced off-target effects in non-treated liver tumors following histotripsy while off cytotoxic therapy. One patient experienced a Grade 3 complication of bacteremia requiring prolonged inpatient admission. No deaths occurred within 30 days.

Histotripsy demonstrates a favorable safety profile for liver metastases. Observed off-target effects in untreated lesions suggest systemic immunomodulatory responses. Further investigation is warranted to elucidate patient-specific factors (e.g., tumor biology, concurrent therapies) that optimize systemic immune activation. Larger prospective studies with longitudinal immune profiling are needed to validate histotripsy's potential dual role as a locoregional therapy and immune primer in metastatic liver disease.

Level 2b, retrospective cohort study.