Summary

Doubling complete histological response in sarcomas with radiation therapy using nanoparticles (Hafnium oxide, NBTXR3), a phase III trial

Summary

Background: Pathological complete response to preoperative treatment in adults with soft-tissue sarcoma can be achieved in only a few patients receiving radiotherapy. This phase 2–3 trial evaluated the safety and efficacy of the hafnium oxide (HfO2) nanoparticle NBTXR3 activated by radiotherapy versus radiotherapy alone as a pre-operative treatment in patients with locally advanced soft-tissue sarcoma.

Methods: Act.In.Sarc is a phase 2–3 randomised, multicentre, international trial. Adults (aged ≥18 years) with locally advanced soft-tissue sarcoma of the extremity or trunk wall, of any histological grade, and requiring preoperative radiotherapy were included. Patients had to have a WHO performance status of 0–2 and a life expectancy of at least 6 months. Patients were randomly assigned (1:1) by an interactive web response system to receive either NBTXR3 (volume corresponding to 10% of baseline tumour volume at a fixed concentration of 53·3g/L) as a single intratumoural administration before preoperative external-beam radiotherapy (50 Gy in 25 fractions) or radiotherapy alone, followed by surgery. Randomisation was stratified by histological subtype (myxoid liposarcoma vs others). This was an open-label study. The primary endpoint was the proportion of patients with a pathological complete response, assessed by a central pathology review board following European Organisation for Research and Treatment of Cancer guidelines in the intention-to-treat population full analysis set. Safety analyses were done in all patients who received at least one puncture and injection of NBTXR3 or at least one dose of radiotherapy. This study is registered with ClinicalTrials.gov, number NCT02379845, and is ongoing for long-term follow-up, but recruitment is complete.

Findings: Between March 3, 2015, and Nov 21, 2017, 180 eligible patients were enrolled and randomly assigned and 179 started treatment: 89 in the NBTXR3 plus radiotherapy group and 90 in the radiotherapy alone group.Two patients
in the NBTXR3 group and one patient in the radiotherapy group were excluded from the efficacy analysis because they were subsequently discovered to be ineligible; thus, a total of 176 patients were analysed for the primary endpoint in the intention-to-treat full analysis set (87 in the NBTXR3 group and 89 in the radiotherapy alone group). A pathological complete response was noted in 14 (16%) of 87 patients in the NBTXR3 group and seven (8%) of 89 in the radiotherapy alone group (p=0·044). In both treatment groups, the most common grade 3–4 reatment-emergent adverse event was postoperative wound complication (eight [9%] of 89 patients in the NBTXR3 group and eight [9%] of 90 in the radiotherapy alone group). The most common grade 3–4 adverse events related to NBTXR3 administration were
injection site pain (four [4%] of 89) and hypotension (four [4%]) and the most common grade 3–4 radiotherapy-related adverse event was radiation skin injury in both groups (five [6%] of 89 in the NBTXR3 group and four [4%] of 90 in the radiotherapy alone group). The most common treatment-emergent grade 3–4 adverse event related to NBTXR3 was hypotension (six [7%] of 89 patients). Serious adverse events were observed in 35 (39%) of 89 patients in the NBTXR3 group and 27 (30%) of 90 patients in the radiotherapy alone group. No treatment-related deaths occurred.

Interpretation: This trial validates the mode of action of this new class of radioenhancer, which potentially opens a large field of clinical applications in soft-tissue sarcoma and possibly other cancers.

Summary

NBTXR3 is a first-in-class Hafnium-Oxide nanoparticle intratumorally (IT) injected. When activated by radiotherapy (RT), it allows for a higher energy deposit than RT alone, yielding an increased tumoral cell death.

A phase I study in soft tissue sarcoma (STS) showed that a single NBTXR3 IT injection at 10% of the baseline tumor volume with preoperative RT was technically feasible with manageable toxicity and clinical activity was observed.

In this international, multicenter, randomized, open-label phase II/III study, patients (pts) with locally advanced STS of the extremity and trunk wall received either a single IT injection of NBTXR3 followed by RT or RT alone (1:1 ratio), both followed by surgical resection. RT was by Intensity Modulated RT or 3D-RT of 2Gy/25 fractions (total 50 Gy). The primary endpoint was the pathological Complete Response Rate (pCRR) defined as the percentage of pts presenting ≤5% of residual viable cancer cells (EORTC guidelines) evaluated by a blind Central Review Board. Key secondary endpoints included negative surgical margins (R0) and safety.

In the intent-to-treat full analysis set population (n=179), which included all pts who were randomized and stratified by STS histological subtype, the pCRR was 16.1% vs 7.9 (p=0.0448) and the R0 rate was 77.0% vs 64.0% (p=0.0424) for NBTXR3+RT and RT alone respectively. NBTXR3 caused injection-site pain in 12 (13.5%) pts. It was also associated with grade 3-4 acute immune reactions in 7 (7.9%) pts, but these adverse events were of short duration, manageable, and resolved spontaneously in some cases. Outside the injection, NBTXR3 was very well tolerated and its safety profile was comparable to RT alone.

NBTXR3 activated by RT was signicantly superior to RT alone and this trial met both primary and secondary endpoint with a positive safety profile. NBTXR3 represents a new option for preoperative treatment for locally advanced STS.