ESTRO 2021 Abstract Book

S1170

ESTRO 2021

Median time from the end radiotherapy to surgery was 33 days (range, 11-74 days). Median pathological response was 87%% (range 15-100%). With a median follow-up of 30 months (3 - 51 months), there were 10 progression and 4 death events. Conclusion RT-CT preoperative have shown relevant clinical activity in ASTS, favorable safety profile and antitumor activity in the preoperative setting of patients affected by ASTS. PO-1424 Combination of pre- and postoperative radiotherapy for soft tissue sarcomas: is it feasible? S. Novikov 1 , G. Gafton 2 , M. Ebert 3 , E. Fedosova 1 , J. Melnik 1 , G. Zinoviev 3 , A. Artemyeva 4 , S. Kanaev 1 1 N.N. Petrov National Research Cancer Center , Radiotherapy, St Petersburg, Russian Federation; 2 N.N. Petrov National Research Cancer Center , Suregry, St Petersburg, Russian Federation; 3 N.N. Petrov National Research Cancer Center , Surgery, St Petersburg, Russian Federation; 4 N.N. Petrov National Research Cancer Center , Pathology, St Petersburg, Russian Federation Purpose or Objective preliminary analysis of single center prospective observation study ( NCT04330456) looking at preoperative stereotactic ablative radiotherapy (SABR) of soft tissue sarcomas followed by surgery and postoperative from 06.2018 to 02.2021 26 patients with soft tissue sarcomas of extremities were included in the protocol and 16 of them had at least 12 months of follow-up and were available for analysis. Preoperative SABR (5 fraction of 5Gy on the margins and 7 Gy in the center) was followed by surgery and postoperative conventional irradiation (25 fractions of 2 Gy). Acute and late adverse events were determined according to Canadian wound complication scale and CTCAE. Results In all patients surgery after pre-operative SABR was performed without delay (in average 20 days) and in all cases wound was healed by primary intention within 51.8 (range, 33-99) days after surgery. Pathohistological examination of the removed tumor indicate good response (>50% necrosis) to SABR in 10 of 16 patients. Postoperative irradiation was performed in 15 of 16 cases; one patient with lung metastases diagnosed after operation was excluded from the protocol. Two (13%) severe complications (skin necrosis and joint stiffness) appeared 1 and 5 months after the end of treatment. We did not see any case of amputation, bone fraction, severe neuropathy or vascular damage. Local recurrences were not recorded within 12-31 months of follow- up. Generalization was diagnosed in 4 patients and manifested by lung meatstases in all cases. Conclusion Combination of preoperative SABR, surgery and postoperative conventional irradiation is a safe and feasible treatment option. conventional irradiation. Materials and Methods PO-1425 the effect of hypofractionated radiotherapy combined with PD-1 blockade for metastatic sarcoma L. XUE 1 , X. Wang 1 , K. Xin 1 , Q. Wang 1 , B. Liu 1 , R. Li 2 1 Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, The Comprehensive Cancer Center , Nanjing, China; 2 Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University Medical School, The Comprehensive Cancer Center, Nanjing, China Purpose or Objective Patients with metastatic sarcoma have limited opportunities for achieving both local and distant tumor control. There is limited evidence demonstrating the efficacy and safety of hypofractionated radiotherapy combined with PD-1 blockades in metastatic sarcoma. Materials and Methods We analyzed 12 patients with metastatic sarcoma (three with bone sarcoma and nine with soft tissue sarcoma) from June 1, 2020-February 5, 2021 in this retrospective case-series. Response Evaluation Criteria in Solid Tumors (RECIST version 1.1) was used to assess tumor control. Acute and chronic toxicity were recorded using Common Terminology Criteria for Adverse Events (CTCAE, version 5.0). Results Median follow-up is 2.4 months. Eight patients ( two with bone sarcoma and six with soft tissue sarcoma) received immunogenic dose hypofractionated radiotherapy (5-8Gy*3f) with concurrent PD-1blockade to 16 sites (eight local tumor and eight distant tumor ). No grade 4 to 5 toxicities were observed. Grade 3 lymphopenia was observed in three (37.5%) patients. Three distant tumor demonstrated local progression and the other sites remained stable or with response. Abscopal effect occurred in one patient diagnosed with small intestine ewing sarcoma. Among the 8 patients, the ORR was 12.5% (1/8) and the DCR was 62.5% (5/8). Four patients (one with bone sarcoma and three with soft tissue sarcoma) received full dose hypofractionated radiotherapy (5Gy*10f) to 9 sites (four local tumor and five distant tumor ) with concurrent PD-1blockade. Two distant tumors demonstrated local progression and the other sites remained stable. Among the 4 patients, the ORR was 0% (0/8) and the DCR was 50% (2/4). There was a single incidence of grade 2 edema which resolved with intervention. Conclusion Hypofractionated radiotherapy combined with PD -1 blockades is safe and effective in local control on metastatic sarcoma patients. Although the incidence of abscopal effects is still low, this modality in metastatic sarcoma merit further study.

PO-1426 Role of 22q12 translocation as a predictor of metastasis and decreased survival in Ewing