International multicenter retrospective study on pleomorphic rhabdomyosarcoma (P-RMS), a PUSH platform study: outcome...

The purpose of this study was to report the outcome of primary localized pleomorphic rhabdomyosarcoma (P-RMS).

Patients with primary localized P-RMS, aged >40 years, and surgically treated with curative intent from January 2013 to December 2023 were enrolled from 25 institutions across 12 countries. Pathological inclusion criteria were predefined by expert pathologists per established World Health Organization guidelines. Primary endpoint was overall survival (OS). Secondary endpoints were disease-free survival (DFS), crude cumulative incidence (CCI) of local recurrence (LR), CCI of distant metastases (DM), post-relapse OS, and post-metastasis OS.

A total of 93 patients were eligible and included in the present study. At a median follow-up of 39.8 months (interquartile range 22.83-85.69 months), 32/93 (34%) patients died and 53/93 (57%) recurred. The corresponding 5-year OS and DFS were 57.7% [95% confidence interval (CI) 46.7% to 71.2%] and 35.8% (95% CI 26.3% to 48.9%), respectively. Younger age, R0 surgical margins, and administration of radiotherapy were positive prognostic factors in multivariable analysis for DFS. LR and DM were developed in 14/93 (15%) and 39/93 (42%) patients, respectively. The corresponding 3-year CCI-LR and DM were 16% (95% CI 8.9% to 25%) and 44% (95% CI 33% to 55%). Post-metastasis median OS was 14.3 months (95% CI 9.4 months-not reached).

While P-RMS is known to be an aggressive histologic sarcoma subtype, one-third of patients with primary localized disease may be cured. The contribution of chemotherapy and radiotherapy to the cure rate remains unclear. Post-metastatic outcomes mirror those observed in other sarcomas.