ESTRO 2023 - Abstract Book

S1267

Digital Posters

ESTRO 2023

Conclusion A positive resection margin has a negative impact on the overall survival and local recurrence of patients with extremity soft tissue sarcomas receiving adjuvant radiotherapy. The absence of a bolus does not seem to worsen the local control, hence should be avoided due to increased frequency of toxicity. Further large-scale research with long-term follow-up is necessary.

PO-1561 Radiation- induced sarcoma after radiotherapy in breast cancer: analysis of a single institution.

M. Cerrolaza 1 , V. Navarro 2 , A. Lanuza 2 , C. Colom 1 , P. Sanagustin 1 , A. Pardo 3 , M. Gascon 3 , A. Campos 4 , R. Ibañez 1

1 University Hospital Miguel Servet, Radiation Oncology, ZARAGOZA, Spain; 2 University Hospital Miguel Servet, Radiation Oncology, ZARAGOZA, Spain; 3 University Clinical Hospital Lozano Blesa, Radiation Oncology, ZARAGOZA, Spain; 4 University Hospital Miguel Servet,, Radiation Oncology, ZARAGOZA, Spain Purpose or Objective Radiotherapy is an integral component of the treatment of patients with primary breast cancer. Radiation-induced sarcoma (RIS) is a rare iatrogenic malignancy that can occur after radiotherapy and is associated with poor outcomes. The most frequent histology is angiosarcoma and the occurrence rate is 0.03%–8%. To be classified as RIS, must be fulfilled that: there must be evidence of an initial malignant tumour of a different histology than the RIS, the second malignancy must histopathologically be a sarcoma; development of the sarcoma must occur in an irradiated field, and there must be a latency period between the two malignancies set at 3 years but cases have been described as occurring within the first 6 months after radiotherapy, There is controversy about the area of appearance, being one of the theories its origin arises at the edge of the radiation fields where the doses are lower. The present study aimed to analyze the cases with RIS after radiotherapy in breast cancer in our institution. Materials and Methods Data were collected from patients diagnosed with RIS who had received previous treatment with adjuvant radiotherapy after breast cancer from 2010-2021. Oncologic history, age, time of sarcoma onset since irradiation, location, treatment received and current status were analysed. Results 5 patients were found with a mean age at RIS diagnosis of 66.2 years. As neoplastic history one of them presented 3 previous neoplasms (bilateral breast cancer and endometrium) and three patients 2 neoplasms (60%) (bilateral breast, and thyroid and breast cancer). The mean latency time between the administration of RT in the primary breast cancer and the diagnosis of sarcoma was 14 years (range 1-27) of which 80% presented histology consistent with angiosarcoma. The diagnosis in two patients arose as cutaneous thickening with multiple cutaneous nodules, one of them as an adenopathic conglomerate and two of them as a nodule in the parasternal region. After the extension study, 2 patients presented multiple distant metastases.