Perioperative outcomes and prognostic determinants in adult spindle cell/sclerosing rhabdomyosarcoma: implications of treatment intensity, surgical margins, and molecular heterogeneity

Background: Spindle cell/sclerosing rhabdomyosarcoma (ssRMS) represents an uncommon and biologically heterogeneous soft tissue sarcoma with clinical outcomes in adults markedly inferior to those in pediatric populations. Perioperative treatment strategies and prognostic factors specific to adult ssRMS remain poorly defined. Methods: A total of 20 adult ssRMS patients treated at a single center were retrospectively identified between 2014 and 2023. All patients underwent surgical resection (R0/R1/R2) and received adjuvant chemotherapy (VAC or non-VAC regimens); postoperative radiotherapy was administered in 14 patients. Kaplan-Meier analysis was employed to estimate survival outcomes; log-rank testing was applied to assess between-group differences; and univariate Cox proportional hazards regression was used to calculate hazard ratios (HRs) and 95% confidence intervals. Results: Median follow-up was 35.9 months (95% CI: 28.4-43.3). Median RFS was 37.9 months (95% CI: 12.8-63.1), with 3-year RFS and OS rates of 65.0% and 74.5%, respectively. R0 resection showed a non-significant directional association with improved RFS, and postoperative radiotherapy showed a non-significant directional association with improved OS. Longer chemotherapy duration (≥12 cycles) was associated with improved OS (P = 0.030), although this finding remains exploratory because no deaths occurred in the ≥12-cycle group. Molecular tests were performed in 13 of 20 patients (65%), identifying MYOD1 mutations in 5 patients and ALK unbalanced translocations in 3 patients. Within the molecularly tested subset, progression and death events were observed only among patients harboring MYOD1 mutations or ALK unbalanced translocations. Conclusion: In this adult ssRMS cohort, multimodality perioperative treatment yielded a median RFS of 37.9 months and a 3-year OS rate of 74.5%.Surgical margins, treatment-related factors, and molecular alterations may contribute to outcome heterogeneity in adult ssRMS. MYOD1 mutations and ALK rearrangements identified subsets with more aggressive disease courses, supporting routine molecular profiling in adult ssRMS. These findings are hypothesis-generating given the small cohort size.