Local Tumor Control of Liver Tumors After Histotripsy: A Preliminary National Multicenter Study

PURPOSE Histotripsy is a noninvasive, nonionizing, nonthermal method of treating liver tumors receiving US Food and Drug Administration (FDA) clearance in October 2023. This study aims to describe histotripsy as a method of achieving local tumor control (LTC) for primary and secondary liver tumors. METHODS All patients receiving histotripsy since FDA clearance (December 2023-December 2024) at four institutions (two academic; two private) with >30 days of active follow-up were included. Patients were classified into palliative intent and complete treatment intent. LTC was assessed using contrast-enhanced imaging on the basis of modified response evaluation criteria in solid tumors (mRECIST) and standardized ablation criteria at postoperative days (POD) 30 and 90. RESULTS Forty-seven patients received intended complete treatment to 91 liver tumors. Three total complications were observed: two cases of skin irritation treated with topical ointment and one case of bacteremia. At 30 days, 95% (n = 86/91) of treated liver tumors were nonviable. Two patients (one each with hepatocellular carcinoma and hepatic adenoma) received repeat treatment between POD30 and POD90, both converted to complete response. Forty-four patients and 85 tumors achieved 90-day follow-up. Three patients demonstrated persistently viable disease at POD90, all who had demonstrated viable tumor at POD30. Thus, the calculated primary efficacy rate at POD90 was 94% (n = 80/85), and the secondary efficacy rate was 96% (n = 82/85). The two patients with viable disease had neuroendocrine (n = 1), breast, and colorectal metastases (n = 1). Control rates were similar between primary and secondary tumors on time-to-event analysis (log-rank P = .146). CONCLUSION Histotripsy achieved high rates of LTC at 30 and 90 days in this preliminary multicenter cohort. Longer-term follow-up is needed to confirm stable results.