S1041
Clinical – Sarcoma, skin cancer, malignant melanoma
ESTRO 2026
Canadian Sarcoma Clinical and Research Collaboration and evaluated tumor volume response, as well as local and oncological outcomes, in patients with PEComa treated with RT. Patients were diagnosed with PEComa between 2005 and 2023 at a single tertiary sarcoma centre. Demographic, clinical, RT, and volumetric tumor data before and after RT were collected. Initial tumor volume (cm ³ ) was determined by contouring the GTV on the pre-RT simulation CT. All available follow-up scans were reviewed. If no change in the largest axial lesion diameter was observed per RECIST v1.1, the GTV was contoured, measured and classified according to RECIST on the last available scan, excluding surgical patients. Local control and overall survival were estimated using the Kaplan-Meier method with log-rank test. Results: In total, 24 lesions in 12 patients were evaluable for the volumetric response analysis, with a median radiological follow-up of 10 months (range: 1-65 months) after RT. Of these, 7 lesions were treated with perioperative RT with curative intent and 17 with palliative intent. Four of seven curative-intent patients required palliative RT later. For 17/24 lesions, patients were treated with systemic agents before RT for the site and systemic treatments during imaging follow-up were administered in 19/24 lesions. Five local failures were observed, with an estimated 1-year local control rate of 76.4% (figure 1). Lesions receiving an equivalent dose in 2 Gy fractions (EQD2, α / β = 5) ≥ 40 Gy had significantly better local control than those receiving <40 Gy (p=0.006). Among the 17 palliative RT lesions treated without surgery, mean tumor volume decreased from 301.5 cm ³ (Standard deviation: 643.6) to 108.3 cm ³ (standard deviation: 205.5) as best response after RT. In the palliative group, four local failures were observed. 76.5% achieved LC for the duration of observed follow up. Of the 13 controlled lesions, stable disease was achieved in 7 lesions and partial response in 6 lesions at last follow up. Seven of the twelve patients (58.3%) died from their disease, with a median overall survival of 46 months after diagnosis.
Conclusion: PEComas appear to be radiosensitive, showing substantial tumor volume reduction and favorable local control particularly with higher RT doses. Nonetheless, overall survival was poor, reflecting the aggressive nature of this disease. Keywords: ultra-rare tumors, radiological response Digital Poster 3117 Radiotherapy in squamous cell skin cancers: current practice and future directions Hajer MNIF radiotherapy, centre Henri Becquerel, rouen, France Purpose/Objective: The management of cutaneous squamous cell carcinoma (cSCC) has evolved rapidly with the advent of immunotherapy. Cemiplimab, a PD-1 inhibitor, has demonstrated significant efficacy in advanced and localized settings. Nevertheless, radiotherapy remains a critical component of curative, consolidative, and palliative strategies. This review aims to outline the current indications and future directions of RT in the cemiplimab era. Material/Methods: Relevant clinical studies and international guidelines from the latest available literature were reviewed to assess the evolving management of squamous cell skin cancers in the cemiplimab era. Results: Cemiplimab has demonstrated substantial efficacy in
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