ESTRO 2025 - Abstract Book

S1712

Clinical - Sarcoma & skin cancer & malignant melanoma

ESTRO 2025

3108

Mini-Oral 949-patient database of Merkel cell carcinoma of the skin: the optimal nodal radiotherapy volume Kurian Joseph 1,2 , Patricia Tai 3 , Michael Veness 4 , Avi Assouline 5 , Jidong Lian 6 , Vimal H Prajapati 7 , Edward Yu 8 1 Radiation oncology, Cross Cancer Institute, Edmonton, Canada. 2 Oncology, U. Alberta, Edmonton, Canada. 3 Oncology, U. Saskatchewan, Saskatoon, Canada. 4 Oncology, U Sydney, Westmead, Australia. 5 Oncology, Centre Clinique de la Porte de Saint-Cloud, Paris, France. 6 Oncology, U Toronto, Toronto, Canada. 7 Dermatology, U Calgary, Calgary, Canada. 8 Oncology, Western U., London, Canada Purpose/Objective: Although Merkel cell carcinoma often spreads to lymph nodes, there is limited research on indications for nodal radiotherapy (NRT). Our objective is to find the optimal radiotherapy nodal volumes for MCC. Material/Methods: A 949-patient database (Mar/1982 - Feb/2015) of six institutions from Canada, France and Australia was built after combining individual data from a PubMed search of the English and French literature. Primary outcome was nodal recurrence, with overall survival as the secondary outcome. Results: In total, 939/949 patients were evaluable, 50.8% of which were male, with a median follow-up of 21 (range: 0-272) months, and a median age of 73 (range: 31-96) years, with 77.5% (728/939) having clinically localized cancer. Among irradiated new (previously untreated) patients, all stages combined, 53% received NRT, 34.9% (80/229) no NRT and 11.8% (27/229) unknown if NRT was given. For recurrent cases, 94.7% (18/19) had NRT while 5.3% (1/19) did not. There were 682 new patients with clinical stage I or II: nodal recurrence was 16% (8/50) with NRT, 40.1% (250/624) without NRT and 1.2% (8/682) uncertain if NRT was given ( P =0.0001, chi-square test with Yates correction [cstYc]). 5 year Kaplan-Meier cause-specific survival was 77.6% vs 60.6% ( P =0.2, logrank test) with/without NRT for these 682 new patients. We then focused on small primary tumors <1 cm, all stages combined, the nodal recurrence was 17.4% (4/23)/24.6% (28/114) with/without NRT ( P =0.6, cstYc). Conclusion: Overall, NRT significantly reduced nodal recurrence. Management of small primary tumors ≤1 cm warrant further investigation with multicenter participation. Keywords: radiotherapy, nodal volume, Merkel cell carcinoma

3340

Digital Poster Radiotherapy for retroperitoneal sarcoma: A rare conundrum

Siddhartha S Laskar 1 , Prachi W Adole 1 , Nehal R Khanna 1 , Jifmi J Manjali 1 , Shraddha Patkar 2 , Mahesh Goel 2 , Bharat Rekhi 3 , Mukta Ramadwar 3 , Suman Ankathi 4 , Akshay Baheti 4 , Jyoti Bajpai 5 , Sushmita Rath 5 , Nilendu Purandare 6 1 Radiation oncology, Tata memorial hospital, Mumbai, India. 2 Surgical Oncology, Tata memorial hospital, Mumbai, India. 3 Pathology, Tata memorial hospital, Mumbai, India. 4 Radiodiagnosis, Tata memorial hospital, Mumbai, India. 5 Medical Oncology, Tata memorial hospital, Mumbai, India. 6 Bioimaging, Tata memorial hospital, Mumbai, India Purpose/Objective: To analyse the outcomes of patients with non-metastatic retroperitoneal sarcoma treated with radiotherapy as a part of multi-modality treatment.