New SIRFLOX analysis shows benefit of SIR-Spheres Y-90 resin microspheres

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A new analysis shows patients with colorectal cancer liver metastases had significantly greater depth of tumour response to Sirtex Medical's (ASX:SRX) SIR-Spheres Y-90 resin microspheres.

The new data was presented by Professor Dr Volker Heinemann in an oral abstract session at the European Society of Medical Oncology’s 18th World Congress on Gastrointestinal Cancer. It suggests patients with liver-dominant mCRC treated first-line with the combination of mFOLFOX6 and SIR-Spheres Y-90 resin microspheres in the recently published SIRFLOX study experienced a more profound response to treatment in the liver than those who received chemotherapy alone.

According to Depth of Response (DpR) analysis, there was a significantly greater Depth of Response (75.0% vs. 67.8% mean reduction in liver tumour burden; p=0.039) in patients who received SIR-Spheres Y-90 resin microspheres combined with chemotherapy. Patients also had a statistically significant, two-month longer time to DpR or maximal tumour shrinkage (median 266 vs. 206 days; p<0.001), compared to those who received chemotherapy alone.

The company said the analysis also revealed that the treatment effect following SIR-Spheres Y-90 resin microspheres was most evident in the patients who entered the study with a greater baseline liver tumour burden.

"This group of more compromised patients, representing over half the patients in SIRFLOX, experienced a statistically significant, 20% greater DpR (77.5% vs. 57.2%; p=0.003) and over three-month longer time to DpR (median 298 vs. 196 days; p<0.001) compared to those treated with chemotherapy alone," said the company. "SIR-Spheres Y-90 resin microspheres was also associated with a doubling of median Progression-Free Survival (PFS) in the liver by competing risk analysis (27.2vs. 13.1 months; p=0.003) in these patients."

"Conversely, patients who had a smaller liver tumour burden (≤12%) on study entry were more than six times more likely to experience a complete response or disappearance of all liver tumours following SIR-Spheres Y-90 resin microspheres compared to those who received only chemotherapy (11.3%vs. 1.7%; p=0.003)," it added.

Professor Heinemann, Professor of Medical Oncology at the Comprehensive Cancer Centre, Ludwig-Maximillian University, Munich, Germany, and European Principal Investigator of the SIRFLOX study, said: “As treatment for metastatic colorectal cancer has improved over the past two decades, life expectancies have increased four-fold. But this increased survival benefit in turn has raised the barrier of proof of efficacy for new therapies or combinations of therapy that have emerged.

“Oncologists have for some time observed that Progression-Free Survival, or PFS, is not always a good predictor of overall survival for patients with metastatic colorectal cancer, as has been seen in some studies with biologic agents,” explained Professor Heinemann. “For this reason, in recent years we have seen an important surge of activity to find better surrogate markers for overall survival in mCRC, particularly regarding the effect of treatment on patients’ Depth of Response. The greater depth of response and time to maximal response following SIR-Spheres Y-90 resin microspheres, together with the prolonged PFS in the liver, are very encouraging and increase our anticipation for the survival data we hope to see in 2017.”