Local Failure in Parameningeal Rhabdomyosarcoma Correlates With Poor Response to Induction Chemotherapy

Abstract

Background Local control remains a challenge in pediatric parameningeal rhabdomyosarcoma (PM-RMS), and survival after local failure (LF) is poor. Identifying patients with a high risk of LF is of great interest to clinicians. In this study, we examined whether tumor response to induction chemotherapy (CT) could predict LF in embryonal PM-RMS. Methods We identified 24 patients with embryonal PM-RMS, age 2 to 18 years, with complete magnetic resonance imaging and gross residual disease after surgical resection. All patients received proton radiation therapy (RT), median dose 50.4 GyRBE (50.4-55.8 GyRBE). Tumor size was measured before initial CT and before RT. Results With a median follow-up time of 4.1 years for survivors, LF was seen in 9 patients (37.5%). The median time from the initiation of CT to the start of RT was 4.8 weeks. Patients with LF had a similar initial (pre-CT) tumor volume compared with patients with local controlled (LC) (54 cm3 vs 43 cm3, P=.9) but a greater median volume before RT (pre-RT) (40 cm3 vs 7 cm3, P=.009) and a smaller median relative percent volume reduction (RPVR) in tumor size (0.4% vs 78%, P<.001). Older age (P=.05), larger pre-RT tumor volume (P=.03), and smaller RPVR (P=.003) were significantly associated with actuarial LF on univariate Cox analysis. Conclusions Poor response to induction CT appears to be associated with an increased risk of LF in pediatric embryonal PM-RMS.

Pencil Beam Scanning Proton Therapy for Pediatric Parameningeal Rhabdomyosarcomas: Clinical Outcome of Patients Treated at the Paul Scherrer Institute

“…), the majority of them (89%) being local failure only. These results are in keeping with other series, which showed that local failure is the greatest obstacle to cure patients with PM‐RMS, with this event happening in 68–75% of patients presenting recurrent or progressive disease . The rate of treatment failure is approximately equivalent to that reported in a modern photon series but substantially less than the reported rate in a recent proton series .…”

“…[20][21][22] The rate of treatment failure is approximately equivalent to that reported in a modern photon [21] series but substantially less than the reported rate in a recent proton series. [20] The explanation for the observed discrepant rates of treatment failure between the two proton series is unclear but could result from imbalances between the two groups with respect to known and unknown baseline prognostic factors or from statistical chance. One of the concerns of PBS-PT is that this treatment modality is very sensitive to changes in the patient's anatomy, which can substantially corrupt the nominal dose distribution, substantially more than with photon RT.…”

“…These results are in keeping with other series, which showed that local failure is the greatest obstacle to cure patients with PM‐RMS, with this event happening in 68–75% of patients presenting recurrent or progressive disease . The rate of treatment failure is approximately equivalent to that reported in a modern photon series but substantially less than the reported rate in a recent proton series . The explanation for the observed discrepant rates of treatment failure between the two proton series is unclear but could result from imbalances between the two groups with respect to known and unknown baseline prognostic factors or from statistical chance.…”

“…). It is substantially longer than the 5‐week IT reported by US groups and reflects the treatment paradigm in Europe . For PM‐RMS, these data suggest that RT should not be unduly delayed and should rather be delivered sooner than later in patients with high‐risk features (i.e., those with meningeal involvement).…”

Pencil‐beam scanning for pediatric rhabdomyosarcoma: Promise and precautions

“…MGH also published a retrospective subset analysis of 24 embryonal PM‐RMS patients treated with passive scatter protons, looking at the correlation between LF and response to induction chemotherapy . In this study, the LF rate for the entire cohort was 37%, raising concerns about the potential for an increased risk of local or marginal failures with protons, due to the rapid dose fall off and high sensitivity to anatomy changes.…”