ESTRO 2025 - Abstract Book

S1660

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

234

Digital Poster Merkel Cell Carcinoma long-term outcomes after radiotherapy treatment. Enar Recalde Vizcay 1 , Begoña Navalpotro 1 , Blanca Peregrin 1 , Carla Ferrandiz 2 , Jorge Hernando 3 , Jaume Capdevila 3 , Raquel Granado 1 1 Radiation Oncology, Vall d'Hebron University Hospital, Barcelona, Spain. 2 Dermatology, Vall d'Hebron University Hospital, Barcelona, Spain. 3 Medical Oncology, Vall d'Hebron University Hospital, Barcelona, Spain Purpose/Objective: Merkel Cell Carcinoma (MCC) is a rare, aggressive disease, with a high relapse rate (1/3) and limited systemic treatment options, resulting in higher fatality rate than melanoma. Radiotherapy (RT) is essential to prevent local relapse (LR), but published large cohorts lack detail on initial and LR therapeutic approaches. We aimed to provide long-term follow-up data after RT treatment. Material/Methods: Single-centre retrospective cohort of 17 patients receiving radical/adjuvant RT between 11/2011-04/2024. All had biopsy-confirmed non-metastatic MCC and underwent multidisciplinary discussion. Data on initial characteristics, management, relapse and survival were collected. Time from first biopsy date. Relapse pre-RT and post-RT considered separately. Palliative-intention RT was not included. Results: Caucasian (100%) patients, mean age 73,7y, with mainly (10/15) head and neck tumors, staged with PET-CT (87%) or CT (13%) received RT as radical (3), adjuvant (9) or both (3) as they presented relapse after surgery (pre-adjuvant-RT). Mean follow-up was 44.1 months (median 42). Five patients (5/17) relapsed, at a mean time of 5.8 months from RT. Four relapses were locorregional but out of RT field, all of them received local salvage therapy (one surgery, the rest radiotherapy again). Three patients received up to three consecutive RT-treatments to locorregional progressions, without presenting need for systemic therapy. The fifth relapse was distant and started Avelumab, as well as palliative intention RT to different sites. Interestingly, two of the patients with relapse after RT had previously relapsed during post-surgery period (prior to adjuvant RT). A total of five patients died, at a mean time of 36.2 months (range 13-42 months). Four out of five (80%) had previously relapsed and had active MCC at the time of death, with two deaths attributed to MCC progression. Only one relapsed patient is considered cured, and received both radical and salvage RT. Progression and death details: Table 1. Survival detail: Figure 1.