Assessing response and adherence to neoadjuvant treatment in soft tissue sarcomas of the extremities.

e23559 Background: The standard treatment for large, intermediate, and high-grade extremity soft tissue sarcoma (ESTS) involves surgery and radiotherapy. The addition of chemotherapy has improved oncological outcomes, such as reduced recurrence and prolonged survival. However, the relationship between neoadjuvant treatment and tumor response in ESTS is not well understood. Pathological evaluation of viable tumor cells after treatment is an indicator of tumor response, yet the proportion of viable tumor cells remains high, particularly in high-risk sarcomas. Combining radiotherapy with chemotherapy may enhance the response of tumor cells. Objective: This study aims to evaluate the effects of neoadjuvant chemotherapy (NCT) and chemoradiotherapy (CRT) on patients with high-risk ESTS and to determine its impact on the pathological response. Methods: We enrolled adult patients with high-risk ESTS (SARCULATOR OS < 60%) at a single center in Latin America. The study was designed to analyze the pathological response in patients with high-risk sarcomas who underwent neoadjuvant CRT and resection and to correlate these responses with various variables. The treatment response was evaluated using the EORTC–STBSG criteria. Results: Thirty-four patients were recruited, with a median age of 44 years (IQR 23-74). Fifty-two percent had T3 tumors (mean size 18 cm), and 79.4% were diagnosed at stage III. The predominant histological subtypes were synovial sarcoma (35.3%) and dedifferentiated liposarcoma (29.4%). The most used NCT regimen was doxorubicin/ifosfamide (84.4%), with 62.5% receiving a dosage intensity of Q4W, affected by overcapacity, and 25% received Q3W. Concurrent CRT was administered to 64.7% of patients, with a median delay to onset of 36 days due to overcapacity (43.5%). Only 79.4% completed three preoperative cycles of treatment. As for the response, 41.2% had an EORTC-E response, and 17.6% had an EORTC-D response. Grade 3 neutropenia and anemia occurred in 17.2% and 8.8% of patients, respectively. Disease progression during NCT was observed in six patients. No significant difference was found in the pathological response between the Q4W and Q3W dosage intensities (p = 0.62). Conclusions: The impact of NCT on pathological responses was not significantly high, which may be due to the predominant histological type in our series. The main cause of treatment delay at our center was due to overcapacity; however, this did not influence the pathological response relative to dose intensity. Additional follow-up assessments are required to determine the influence on relapse-free and overall survival based on the response after preoperative CRT.