Radiologic and Pathologic Response Evaluation After Neoadjuvant Chemotherapy for Primary Retroperitoneal Sarcoma: A Transatlantic Australasian Retroperitoneal Sarcoma Working Group (TARPSWG) Collaboration.

Background: Comsplete resection is the primary treatment for retroperitoneal sarcomas (RPS). The role of neoadjuvant chemotherapy (NACT) in improving oncologic outcomes is currently under investigation in the STRASS 2 trial. This study assessed the association between change in tumor size or pathologic response and oncologic outcomes.

Methods: Data were retrieved from the international Retroperitoneal Sarcoma Registry and included patients who had RPS treated with NACT between January 2017 and October 2020. The correlation between radiologic response (RECIST1.1), change in tumor size, pathologic response, and oncologic outcomes was evaluated. Binary logistic, Cox, and polynomial spline regression and log-rank tests were performed as statistical analyses.

Results: The study enrolled 141 patients from 14 medical centers. The most common histologies were dedifferentiated liposarcoma (36.9 %) and leiomyosarcoma (34 %). At completion of NACT, 14.5 % of the patients, had a partial response (PR), 63.3 % had stable disease (SD), and 22.2 % had progressive disease (PD). The hazard ratio of PD after NACT for overall survival (OS) was 1.9 (95 % confidence interval [CI], 0.9-4.1). A linear trend was observed between tumor growth and death rate. At early radiologic evaluation during NACT, PD was significantly associated, with worse OS (HR, 5.4; 95 % CI, 1.1-25.3). Partial response was significantly correlated with ≥20 % fibrosis/hyalinization (odds ratio [OR], 5.6; 95 % CI, 1.1-29.0).

Conclusion: Progression in RPS on an early evaluation scan is associated with worse OS, and radiologic response is correlated with pathologic response based on fibrosis/hyalinization. A larger cohort is necessary for more significant associations between radiologic or pathologic response and oncologic outcomes.