Sirtex Medical (ASX:SRX) shares are down slightly today after its radioactive microspheres failed to meet the primary endpoint in a liver cancer trial.

The company’s SIR-Spheres Y-90 resin microspheres did not improve survival in patients with advanced hepatocellular carcinoma compared to a group treated with the current standard of care, sorafenib.

Data from the 360-patient trial were presented at the annual meeting for the American Society of Clinical Oncology.

“We found that the Asian patients with locally advanced HCC who were treated with Y-90 resin microspheres had a significantly better tumor response rate of 16.5% compared to 1.7% for sorafenib in the intent to treat, or ITT analysis, and 23.1% for SIRT compared to 1.9% in the treated population, which represents the patients who actually received their allocated treatment. They also experienced almost a 2-fold decrease in severe adverse events compared with those treated with sorafenib,” principal investigator Dr. Pierce Chow said in prepared remarks.

“The primary endpoint of the study, overall survival was not met. If you look at patients assigned to each therapy in the ITT, analysis, median survival in the Y-90 resin microspheres study arm was 8.84 versus 10.02 months for the sorafenib group. This difference is not statistically significant. However, this analysis does not take into account that more than a quarter of the patients who were scheduled to received Y-90 therapy actually didn’t receive treatment. If you look at the survival data based solely on those patients who actually received Y-90 resin microspheres, median OS was 11.3 months compared to 10.4 months for those treated with sorafenib, an opposite trend that is also not statistically significant.”

The company pointed out that the group treated with Y-90 microspheres had fewer side effects, but added that the incidence rate was not significantly different from the sorafenib group.

Sirtex said that patients who received Y-90 resin microspheres experienced additional treatment benefits, such as improved overall progression-free survival and overall time to progression.

These results are consistent with data from a 459-patient trial published in April this year. Survival differences between the 2 groups in that trial were also not significant.

In mid-May, SRX shares tumbled more than 25% after data from a trial showed that the Y-90 microspheres had no effect in improving survival in patients with colorectal cancer.