ESTRO 2024 - Abstract Book

S2105

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

Soft tissue sarcomas are a rare type of cancer, representing 1% of malignant tumors. Approximately 116 new cases are treated per year at the Instituto Nacional de Cancerología. These tumors have high local recurrence rates that can reach 50% at 5 years and a 5-year overall survival ranging from 12 to 70%, depending on the location and histological type. Surgery is the mainstay of treatment in STS; its main objective is to achieve negative oncological margins to reduce the risk of local relapse and, therefore, impact OS. The main operational challenge involved in the administration of optimal doses of RT is that they are higher than the maximum tolerable doses by the organs at risk. Intraoperative radiotherapy appears as an alternative in treating patients with STS, allowing reinforcement to complete the required therapeutic doses, always combined with neoadjuvant or adjuvant EBRT. The present study describes the experience of the Functional Unit for Breast and Soft Tissue Tumors of the INC in using IORT in patients with extremity and retroperitoneal STS over 9 years.

Material/Methods:

An observational, descriptive, and retrospective cohort study that included patients with confirmed diagnosis of extremity or retroperitoneal soft tissue sarcomas, primary or recurrent, who underwent surgical resection and intraoperative radiotherapy, in addition to neoadjuvant or adjuvant external beam radiotherapy, at the Functional Unit for Breast and Soft Tissue Tumors of the Instituto Nacional de Cancerología (INC) (Bogotá, Colombia) between January 2009 and December 2018.

Results:

In Latin America, only few centers use IORT. To date, this is the first report that examines the results of the experience of using IORT with electrons in patients with extremity and retroperitoneal STS treated in a Latin American reference cancer center. When comparing the results of this cohort, in patients with extremity STS, local control rates were 86.6% and 79% at 3 and 5 years, respectively, a figure lower than that reported in the world literature, where the combination of limb-sparing surgery associated with IORT and EBRT shows local control rates at 5 years between 82% and 97%. This can be explained by the fact that the majority (58.8%) of the patients included in our study had unfavorable tumor biological factors with mostly grade II and III tumors, as well as due to