Sirtex reports SIR-Spheres Y-90 resin microspheres failed to improve OS in metastatic colorectal cancer

Sirtex on Thursday said results from an analysis indicated that the combination of chemotherapy plus selective internal radiation therapy (SIRT) using its SIR-Spheres Y-90 resin microspheres did not significantly increase overall survival (OS) in patients with unresectable metastatic colorectal cancer (mCRC), compared with chemotherapy alone. Company shares fell almost as much as 30 percent on the news.

Gary Donofrio, senior vice president for the Americas at the company's Sirtex Medical subsidiary, remarked that "while these results are not what we expected, we believe that SIR-Spheres Y-90 resin microspheres will continue to play an important role in the treatment of patients with mCRC." He added that we "look forward to additional validation of this potentially significant finding to improve survival in patients with right-sided colon cancer in the first-line setting."

The company said the combined FOXFIRE analysis, which will be presented at the American Society of Clinical Oncology (ASCO) annual meeting on June 5, is comprised of data from the SIRFLOX study, which was first unveiled in 2015, as well as data from the new FOXFIRE and FOXFIRE-Global studies. The safety profile "was consistent with what has been previously reported for SIR-Spheres Y-90 resin microspheres in combination with chemotherapy," Sirtex said.

Meanwhile, the company stated that secondary analyses of data from SIRFLOX and FOXFIRE Global show a significant 4.9-month improvement in median OS among patients with right-sided primary colon cancer receiving the SIR-Spheres plus chemotherapy, compared with chemotherapy alone. Donofrio suggested that "if our initial findings are confirmed, a five-month improvement in median survival in the first-line setting could be seen as clinically meaningful in this difficult-to-treat population with liver metastases." Sirtex noted that these data will be presented at the World Congress of GastroIntestinal Cancers next month.

While interim CEO Nigel Lange indicated that "Sirtex intends to examine all aspects of our business following the data," the results are nonetheless expected to have "minimal impact on our current business," as the patients the company targeted had already failed all standard chemotherapy treatments. "In our existing market of salvage…[treatment] there is a market opportunity of 42 000 [colorectal cancer] patients," he said. Lange added "there will be no impact to any of our regulatory approvals globally from this study outcome."

Last month, Sirtex announced data from the 459-patient SARAH study showing that local treatments of advanced or inoperable hepatocellular cancer with SIR-Spheres Y-90 resin microspheres did not significantly increase OS compared to daily standard-of-care systemic therapy with Bayer's Nexavar (sorafenib), but that they were associated with significantly fewer severe treatment-related adverse effects.

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