560 - Longer-term Outcomes Post Histotripsy of Liver Tumors: Lessons Learned and Next Steps

Purpose: Histotripsy is a rapidly expanding minimally-invasive treatment option for non-resectable liver tumors sought after by patients. The Theresa trial was the first in-human trial looking at immediate post-operative technical success and safety profile at 2 months prost-procedure {1}. The subsequent #HOPE4LIVER trial looked at outcomes in 44 patients, but only up to 30 days post-procedure {2}. The purpose of our study is to analyze the long-term efficacy and safety of histotripsy in the treatment of various liver tumor histologies.

Materials and Methods: This is a single-institution retrospective analysis of patients who underwent image-guided histotripsy of nonresectable liver tumors between September 2024 and March 2025. Patients who underwent partial treatment or were lost to follow-up were excluded. Patients treated less than 3 months from the time of data analysis were not included to ensure adequate follow-up. Patients underwent imaging and clinical evaluation immediately post-procedure, at 1 month and every 2-3 months thereafter. Primary clinical endpoint was local tumor control. The safety endpoint included any procedure-related adverse events (AEs) in the study time-period.

Results: A total of 23 patients underwent treatment of 41 non-resectable liver tumors. Average age was 68 years old (48% male, 52% female). Average treated tumor size was 2.6 with an average treatment/cavitation diameter of 4.6 cm. Combined local tumor control at 1 month, 3 month, and 6 month was 79%, 17%, and 0% respectively. Stratified 3-month local control per primary tumor histology was 67% for colorectal adenocarcinomas, 33% for cholangiocarcinomas, 13% for pancreatic ductal adenocarcinomas, and 0% for both hepatocellular carcinomas and neuroendocrine tumors. During the 3 months post-procedure, 100% of successfully treated patients were still alive with a 3.5-month overall survival of 85%, thus far. Three clinically significant AEs occurred. One patient was re-hospitalized for sepsis related to treatment (SIR moderate AE). A second patient developed hepatic vein thrombus immediately post-procedure (SIR moderate AE). A third patient developed severe post-procedure liver hemorrhage resulting in ICU level of care and two emergent embolization interventions (SIR life-threatening AE).

Conclusion: Ongoing monitoring of long-term outcomes of histotripsy is essential for optimization of treatments and patient selection. As seen in this study, new life-threatening AE have occurred reinforcing the importance of continued monitoring and reporting of adverse events.