The first full year of histotripsy for liver tumors: Local tumor control and preliminary oncologic efficacy

Histotripsy is a novel, nonionizing, nonthermal, noninvasive method using focused ultrasound waves to mechanically destroy liver tumors. It received FDA clearance in October 2023. We report the first years' experience at our academic center including, to our knowledge, the first evidence of medium-term oncologic efficacy, reporting local tumor control with this novel approach.

All patients receiving histotripsy were included (December 20, 2023-November 30, 2024). Contrast-enhanced postoperative day 1, 30-, and 90-day scans are obtained in all patients. Tumor viability was determined by Response Evaluation Criteria in Solid Tumours/modified Response Evaluation Criteria in Solid Tumours criteria. Viable tumor on postoperative day 1 imaging was considered inadequate treatment; patients with nonviable tumors on postoperative day 1 were assessed for tumor control at postoperative day 30 and 90. Tumors with intentional partial treatment of a lesion were excluded from local control analyses. Palliative intent treatment refers to attempted immunologic antitumor priming and is pursued in very advanced tumor cases with no chance at curative therapy. All systemic therapy and anticoagulation are continued in the periprocedural period.

In all, 109 lesions in 71 patients were treated with histotripsy, with 9% receiving curative intent treatment and 66% treated palliatively. Among those treated with curative intent, 70% showed nonviable lesions at both 30- and 90-day follow-ups, suggesting effective tumor ablation. Overall, 75% of treatments were aimed at complete lesion ablation. Complications were rare, with only 1 (1%) classified as Clavien grade ≥3. In cases of proper targeting, tumor control was excellent: 60 lesions were nonviable on postoperative day 1, all demonstrating nonviable tumors at 30 days. Among these, 23 also had postoperative day 90 imaging; 100% maintained tumor nonviability. Unfortunately, lesion targeting was imperfect, with 60 (74%) of the 82 lesions intended for complete treatment demonstrating postoperative day 1 tumor nonviability. Notably, 19 (23%) of the 82 lesions were treated with palliative intent, whereas 3 (4%) were treated with curative intent. Ten patients were treated with curative intent; 70% (n = 7) had nonviable tumors on postoperative day 1. All such patients demonstrated persistent nonviability on postoperative days 30 and 90. Thus, 70% of patients treated with curative intent achieved no evidence of disease with 1 treatment, whereas 30% had persistent disease. Of these 3 cases, 2 were retreated with histotripsy and converted to no radiologic evidence of disease, with a total rate of no evidence of disease at 90%. There was a slight, although not significant improvement in targeting as providers gained more experience.

Histotripsy is a safe procedure that is starting to demonstrate promise in effectively controlling local tumors when lesions are accurately targeted. Our collective efforts should focus on education and technical advancements to improve lesion targeting, ensuring that complete treatments are genuinely thorough, although we do note that the targeting success rate may relate to the palliative nature of most treatments. This situation mirrors the initial reports from the ablation literature and is likely to improve with learning curve.