NBTXR3 with radiotherapy doubles responses for soft tissue sarcoma

A trial assessing NBTXR3 plus radiotherapy met its primary endpoint of improved pathologic complete response rate compared with standard of care among patients with soft tissue sarcoma, according to the agent’s manufacturer.

NBTXR3 (Nanobiotix) is a first-in-class product that physically destroys cancer cells when activated by radiation therapy.

In a phase 2/phase 3 study, researchers randomly assigned 180 patients with locally advanced soft tissue sarcoma to NBTXR3 activated by radiotherapy or radiotherapy alone.

Pathologic complete response rate — defined as rate of patients showing less than 5% of residual viable cancers cells posttreatment — served as the primary endpoint.

In the intent-to-treat population, 16.1% of patients randomly assigned NBTXR3 achieved a pathologic complete response compared with 7.9% of patients assigned radiotherapy alone (P = .0448).

Patients randomly assigned NBTXR3 plus radiotherapy also demonstrated a statistically significant increase in surgical margin rate (defined as R0) compared with the control group (P = .042).

“I am amazed by the difference of response rate; it is extremely uncommon to double the rate of complete histological response, and I do not see any other strategy able to accomplish that,” Jean-Yves Blay, MD, director of the Centre Léon Bérard in France, said in a press release. “Even more impressive is the R0 rate, which is increased by more than 20% compared to an average rate of 64%. This difference is really impressive, considering that R0 impacts patients’ relapses and survival.”

The regimen appeared well tolerated, with similar rates of radiation-related adverse events observed in both arms. Researchers observed injection site pain among 13.5% of patients. In addition, 6.7% of patients experienced grade 1 injection site hematoma/ecchymosis. Researchers observed less serious adverse events regarding long-term toxicity in the NBTXR3 arm.

“This study substantiates the medical benefit of safely enhancing the effect of radiation therapy with novel physics-based approaches delivered locally within the cancer,” David Raben, MD, professor of radiation oncology at University of Colorado Cancer Center, said in the release. “In addition, this product may potentiate a proinflammatory environment suitable for immune-enabling or DNA damage inhibitor drugs. These findings set the foundation for additional studies in areas such as head and neck cancer and perhaps in areas such as high-risk prostate, bladder or pancreas cancer.”