MIRRORS-FROZEN: a pilot randomised controlled trial (RCT) comparing open versus robotic surgery in the management of women with complex pelvic adnexal masses ≤ 8 cm—trial protocol

Background Open surgery is the standard of care for suspicious complex adnexal pelvic masses, usually combined with intraoperative frozen section analysis. These lesions may be benign, borderline, or cancerous and are often partly solid and partly cystic in nature. Risk stratification using imaging and tumour markers may be performed preoperatively. To date, no randomised controlled trial (RCT) has compared robotic minimally invasive surgery with open surgery, and existing guidelines primarily focus on the subset with confirmed cancer. Methods This is a single-centre feasibility study (pilot RCT) conducted at the Royal Surrey NHS Foundation Trust in the UK. The trial aims to recruit patients with isolated complex adnexal lesions suspicious for cancer and measuring ≤ 8 cm. Participants are randomised in a 2:1 ratio to either the robotic surgery (study arm) or standard open laparotomy. Intraoperative frozen section analysis guides the extent of surgery in both arms, with no blinding to participants or surgeons. The primary outcomes are recruitment rate, acceptability of randomisation, and questionnaire response rate at predefined assessment time points. Secondary outcomes include conversion from robotic to open surgery, cyst rupture rate, surgical and perioperative morbidity, patient-reported outcomes, and cost analysis. Recruitment will take place over 24 months, with a 6-week follow-up period and a target sample size of 25 participants. Discussion Progression to a definitive trial will be based on predefined feasibility criteria, including a recruitment rate of > 60% of eligible patients, minimal withdrawal due to randomisation (< 20%), and acceptable adherence to allocated intervention, with > 50% of patients in the MIRRORS-FROZEN arm undergoing robotic cyst removal. The study will provide feasibility parameters to inform the design, sample-size calculation, recruitment timeline, and selection of appropriate outcomes for a future adequately powered multicentre non-inferiority RCT focusing on oncological outcomes in the cancer subgroup. Trial registration ClinicalTrials.gov NCT06638593.