2188 - Factors Contributing to Recurrence in Soft Tissue Sarcomas

Purpose/Objective(s): The successful management of soft tissue sarcomas (STS) is often limited by high rates of distant metastases combined with ineffective and toxic systemic therapy regimens. Immunotherapy (IT) is emerging as a promising adjunct. In this study, we aimed to identify patient- and tumor-specific factors that influence recurrence in our population who received radiation (RT).

Materials/Methods: This is a single-center, retrospective, observational study evaluating patients who completed a course of pre- or post-operative RT for localized STS. Factors such as size, histology, grade, percentage of necrosis on surgical pathology, total duration of RT, time between RT and surgery, and receipt of chemotherapy were assessed. The primary endpoint was any recurrence event, including local (LR)/distant recurrence (DR) or recurrence-related death.

Results: Between July 2008 and November 2024, 59 patients were treated with pre-operative and 55 with post-operative RT for localized STS. In pre-operative patients, the average age was 56.5, average tumor size was 12.0 cm, 4 (7.0%) had positive surgical margins, and most (68.0%) were grade 3. The patterns of failure analysis revealed 16 (27.1%) DR-only, 1 (1.7%) LR-only, 4 (6.8%) with both LR and DR, and 3 (5.1%) recurrence-related deaths during a 20.2-month median follow-up (range 0.3 - 189.2). Although not statistically significant, compared to patients with tumor grades 1–2, those with grade 3 faced a 3.3 times higher risk of recurrence while controlling for other variables (HR 3.3, CI 0.86-12.73, p = 0.08). No patient with a positive margin had a LR, while 2 had a DR. In patients treated post-operatively, the average age was 53.7, average tumor size was 10.0 cm, 18 (32.7%) had positive surgical margins, and most (60.4%) were grade 3. There were 12 (21.8%) DR-only, 4 (7.3%) LR-only, 8 (14.5%) both DR and LR, and 4 (7.3%) recurrence-related deaths during a 21.2-month median follow-up (range 0.7-134.7). After adjusting for other factors, large tumor size was significantly associated with recurrence risk (HR 1.07, CI 1.0-1.14, p = 0.03), and there was a trend toward higher recurrence risk with high grade (HR 2.70, CI 0.9-8.17, p = 0.08). Of the 19 patients with positive margin, 4 had LR-only, 3 had DR-only and 2 had both LR and DR. Significantly more patients who got post-op RT vs pre-op RT had positive margins (p < 0.001), although this did not correlate with recurrence.

Conclusion: Most STS recurrences were distant regardless of RT timing. Positive margins were significantly more common in the post-operative RT group. High grade showed a trend for recurrence in both treatment groups, while larger tumor size was significantly predictive for recurrence in those treated post-operatively. Recognizing these risk factors may help inform patient selection for future immunotherapy studies.