Reported side effects from treatment in a prospective phase II randomised trial evaluating local control after stereotactic body radiotherapy (SBRT) vs microwave ablation (MWA) in patients with colorectal liver metastases and oligometastatic disease.

e15522 Background: MWA is considered the treatment of choice for colorectal liver metastases in selected patients with small tumors and/or severe comorbidity excluding liver resection. The role of SBRT for colorectal liver metastases is called for by guidelines. In December 2024 we finished inclusion of one hundred patients in the first prospective randomised trial evaluating freedom from local lesion progression one year after MWA vs. SBRT in patients with colorectal liver metastases (NCT03654131). Methods: From January 2019 to December 2024, 100 patients with 1-3 colorectal liver metastases (diameter < 4.0 cm) were randomised to either SBRT or MWA. Prior to randomization patients were considered eligible for MWA with a curative intent by a multidisciplinary team (MDT). Only patients considered eligible for MWA after ultrasonic evaluation of the liver and eligible for SBRT after magnetic resonance imaging (MRI) of the liver were included. Extrahepatic disease and/or primary tumors were allowed in case of a curative treatment plan. Chemotherapy within three months was allowed. MWA was performed either percutaneously or as an open surgical procedure. SBRT was performed on a CT accelerator after implementation of gold markers or non-invasively using a MRaccelerator. Side effects were reported using Common Terminology Criteria for Adverse Events (CTCAE) v 5. 0. Results: Of the one hundred enrolled patients, 92 patients were treated; 39 with SBRT (34 (87%) on a MRaccellerator) and 53 with MWA (11 (21%) patients with open ablation). Baseline characteristics (male sex 61%, median age 71, (range 40-89)) were similar between both treatment arms. Eight patients were excluded after randomization; one due to secondary cancer, three due to progressive disease and four patients due to surgical resection after randomisation. Eighteen of the 92 patients (20%) patients reported side effects after SBRT or MWA; 4 patients had grade 1-2 nausea, 6 patients had grade 1-2 tiredness and 9 patients had grade 1-4 pain. Three patients experienced grade 3-4 pain; two patients with infection after open MWA and one patient with perforation of the bowel after percutaneous MWA. Pain was non-significantly higher in patients undergoing MWA than SBRT, eight patients vs. one patient, p = 0,07 . Nausea and tiredness were related to resent chemotherapy in 9/10 (90%) patients. Conclusions: Side effects are few after both MWA and SBRT for treating liver metastases in colorectal cancer patients. Pain after SBRT is rare. The primary end point freedom from local lesion progression is awaiting follow-up. Clinical trial information: NCT03654131 .