RECIST Responses to Radiation in Retroperitoneal Soft Tissue Sarcoma: When and How Often Do They Occur?

Area of Science:

• Oncology
• Surgical Oncology
• Radiation Oncology

Background:

• Retroperitoneal sarcoma (RPS) presents challenges for complete surgical resection due to tumor size and adjacent organ invasion.
• Neoadjuvant radiation is explored as a strategy to facilitate surgical resection by reducing tumor dimensions.

Purpose of the Study:

• To investigate the association between neoadjuvant radiation therapy and tumor downsizing in patients with retroperitoneal sarcoma.
• To evaluate the impact of neoadjuvant radiation on tumor size and RECIST response prior to surgical resection.

Main Methods:

• Retrospective review of adult, nonmetastatic RPS patients treated with curative intent between 2000-2020.
• Radiological assessment of tumor size changes (absolute and relative) and RECIST response before and after neoadjuvant radiation.
• Subgroup analyses based on RECIST response were conducted.

Main Results:

• Of 22 patients, 63.6% experienced tumor decrease (mean 7.1% relative decrease), while 36.4% saw no change or an increase (mean 21.9% relative increase).
• The majority of tumors (77.3%) showed stable disease by RECIST criteria; 18.2% demonstrated progressive disease with significant size increase.
• Neoadjuvant radiation did not alter organ abutment or planned multivisceral resections in most cases.

Conclusions:

• Favorable RECIST responses and significant tumor downsizing are uncommon with neoadjuvant radiation for RPS.
• A notable proportion of RPS tumors increase in size during neoadjuvant therapy, challenging its utility for pre-operative downsizing.
• Findings suggest caution in employing neoadjuvant radiation for RPS solely to alter operative plans or achieve tumor reduction.