(P 070) COMPLETE PATHOLOGICAL RESPONSE AFTER NEOADJUVANT TREATMENT IN SOFT TISSUE SARCOMA. A SINGLE INSTITUTION EXPERIENCE.

Objective: Pathological complete response (pCR) to preoperative treatment has been reported as a prognostic factor for survival in the soft tissue sarcoma (STS) population. pCR evaluation has been demonstrated in breast and head and neck cancers widely associated with improved outcomes, including overall survival (OS). The assessment to pathological response is not easily subject to variability, can be globally equitable, and has the potential to serve as a surrogate endpoint for research and survival outcomes.

Methods: This is a retrospective, single-institution study. The inclusion criteria were: patients with STS diagnosed between 2011–2021, s/p neoadjuvant treatment, and pCR (defined as necrosis rate on surgical specimen ≥ 90%). This study was approved by the University of Miami-Sylvester IRB.

Results: We identified a total of 39 patients that met our inclusion criteria. 43% of the population were women. Mean age at diagnosis was 59 years old (range 20-84). 90% of the population remains alive, with mean overall survival of 6.6 years. Disease recurrence (local and distant) was present only in 11 patients (28%) and 4 of these patients (36.3%) progressed to death. Median progression free survival (PFS) was 42.5 months (95% CI 33.9-53.1). 34% of the cohort had the myxofibrosarcoma histology, and this group had mean OS of 7.2 years and mean PFS of 5.8 years. 20% of the myxofibrosarcoma patients developed metastatic disease versus 21% among patient with different histology (p=0.89). Among the neoadjuvant treatments delivered, 93% of the patients received a combination of chemotherapy and radiation. The most common neoadjuvant chemotherapy regimen was the combination of Doxorubicin with Ifosfamide (66% of the patients) and their mean OS was 6.2 years vs 2.9 for the other regimens (p=0.08). Among patients that received neoadjuvant chemotherapy, the median number of preoperative cycles was 4 (SD=1.1). The median time from the start of chemotherapy to surgery was 5 months (SD=1.4 months).

Conclusion: Treatment induced pathologic necrosis has been proven as a predictor of survival in patients with STS in multiple studies. Interestingly, the most common histology present was myxofibrosarcoma, suggesting a good response to neoadjuvant treatment in this group with a lower rate of metastatic disease after pCR, when compared to the literature (35%). Chemotherapy associated with radiation in the neoadjuvant setting was the most common treatment and Doxorubicin with Ifosfamide was associated with a longer OS. The rate of necrosis after surgery has been shown to be a prognostic factor for STS, therefore there is a need to evaluate which associated factors lead to pCR. Further research with the evaluation of the molecular profiling of STS with pCR is underwork to better understand the mechanisms behind treatment responses and we hope to present our data on upcoming CTOS 2023.