New SIRFLOX Analysis Shows Greater Depth of Tumor Response Using SIR-Spheres Y-90 Resin Microspheres
July 12, 2016—Sirtex Medical Ltd announced the presentation of new data that suggest that patients with liver-dominant metastatic colorectal cancer (mCRC) who underwent first-line treatment with mFOLFOX6 and SIR-Spheres yttrium-90 (Y-90) resin microspheres in the SIRFLOX study experienced a much more profound response to treatment in the liver than those who received chemotherapy alone.
Prof. Volker Heinemann, MD, presented the new data at the European Society of Medical Oncology’s 18th World Congress on Gastrointestinal Cancer held June 29 to July 2 in Barcelona, Spain. Prof. Heinemann is Professor of Medical Oncology at the Comprehensive Cancer Centre, Ludwig-Maximillian University, Munich, Germany, and European Principal Investigator of the SIRFLOX study.
The investigators used depth-of-response (DpR) analysis, a relatively new methodology that has been shown to correlate with overall survival and postprogression survival in earlier mCRC studies. The DpR concept and methodology were developed by Prof. Heinemann and his colleagues, in collaboration with other experts in treating colorectal cancer.
The SIRFLOX DpR analysis includes a volumetric model to estimate each patient’s spherical liver tumor volume, based on the length of up to five target liver tumors, which were selected during a central independent blinded imaging review of the patients’ baseline and subsequent radiographic images. DpR was then measured by tracking tumor shrinkage until it reached its lowest point, or nadir.
In previous DpR analyses of the FIRE-3 study with the biologic agent cetuximab, Prof. Heinemann observed a statistically significant correlation between DpR and overall survival. This observation has also been supported by an evaluation of the TRIBE study.
The company reported that there was a significantly greater DpR in patients who received SIR-Spheres Y-90 resin microspheres combined with chemotherapy (mean reduction in liver tumor burden, 75% vs 67.8%; P = .039). Patients also had a statistically significant, 2-month longer time to DpR or maximal tumor shrinkage compared to those who received chemotherapy alone (median, 266 vs 206 days; P < .001) .
The analysis also revealed that the treatment effect after SIR-Spheres Y-90 resin microspheres was most evident in the patients who entered the study with a greater baseline liver tumor burden (> 12% of the liver having been replaced by tumor, a predetermined statistical cut-point to identify potential predictors of DpR). This group of more compromised patients, who represented more than half the patients in SIRFLOX, experienced a statistically significant, 20% greater DpR (77.5% vs 57.2%; P = .003) and over 3-month longer time to DpR (median, 298 vs 196 days; P < .001) compared to those treated with chemotherapy alone.
Treatment with SIR-Spheres Y-90 resin microspheres was associated with a doubling of median progression-free survival in the liver by competing risk analysis in these patients (27.2 vs 13.1 months; P = .003). Conversely, patients who had a smaller liver tumor burden (≤ 12%) on study entry were more than six times more likely to experience a complete response or disappearance of all liver tumors after SIR-Spheres Y-90 resin microspheres compared to those who received only chemotherapy (11.3% vs 1.7%; P = .003).
The predictive value of this approach may be corroborated when overall survival data on the combined SIRFLOX, FOXFIRE, and FOXFIRE Global studies of the association of mFOLFOX6 and SIR-Spheres Y-90 resin microspheres in the first-line treatment of mCRC become available in 2017, advised the company.