Reassessment of trial data at ASCO to benefit Sirtex's cancer-fighting microspheres

Sirtex Medical's SIR-Spheres (green) being delivered into the bloodstream via microcatheter.

Sirtex Medical's SIR-Spheres are a salvage treatment for liver cancer patients, meaning the microspheres are used once chemotherapy has failed. And at the American Society of Clinical Oncology meeting in Chicago the company successfully applied a salvage treatment to a clinical trial that failed to meet its primary endpoint in March.

The same study that sent Sirtex's stock tumbling by more than 50% on the Australian Stock Exchange, sent its price up by 27% following a reassessment of the data at ASCO. After shedding some of that initial gain, the stock is now priced around A$30, compared to A$40 prior to the March news, but that's still better than its low of $A17 in the immediate aftermath of the negative data dump. Note that the stock had already recovered to around A$27 prior to the ASCO presentation.

The news comes amid rumors that Germany's Bayer is considering making a bid for the company.

In March Investors fretted that the SIR-Spheres did not demonstrate a statistically significant improvement in overall progression-free survival from tumors in any organ or body site among patients with non-resectable metastatic colorectal cancer (mCRC). At the time, Sirtex said the SIR-Spheres did improve progression-free survival in liver tumors, and at ASCO, the company quantified the results of its secondary endpoint, saying they improved the metric by 7.9 months.

"We found that while liver tumors began to grow again after a median of 12.6 months in patients with mCRC who received only first-line chemotherapy, those who also received first-line treatment with SIR-Spheres Y-90 resin microspheres had their liver tumours controlled for a median of 20.5 months," said the study's co-principal investigator, Peter Gibbs, of Australia's Royal Melbourne Hospital, during his presentation at ASCO, according to a Sirtex release.

Investors increasingly believe that the microspheres can make a mark among patients in the subgroup of mCRC patients whose tumors are restricted to the liver, where the new information could help them shed their salvage therapy status.

"We believe Sirtex has inspired early adopters to treat a significant subgroup of liver cancer as first-line, with others clearly encouraged to look at second-third-line treatment," investment bank UBS advised its clients, according to The Sydney Morning Herald.

"This allows Sirtex to target up to 40 per cent of patients where the colorectal cancer has been resected but the disease remains in liver only," the broker said. "It is likely that this category would be narrowed again to those who are fit and healthy and where there is an adverse molecular signature." It believes Sirtex can expand its market size by 4- to 16-fold, and increase its market penetration from a base of 7-8% of the addressable market.

Others analysts are still bearish on the company, and question whether the time to regrowth of liver tumors has an impact on actual patient survival, according to an Australian investment news website. Data on quality of live and patient survival will be released from another clinical trial in 2017.

Sirtex's SIR-Spheres are used to transport the radioactive element yttrium-90, which delivers beta radiation over a short distance (2.5 millimeters) at the site of liver tumors.

The SIR-Spheres are inserted into the liver's hepatic artery using a microcatheter that travels through the leg's arteries. The spheres reach the liver tumor through the tumor's arterial blood supply. They then become implanted in the tumor because, at a median diameter of 32 microns, they are too large to pass through small blood vessels within the tumor, Sirtex says in a video on its website.

Then, the radiation begins. More than 90% of the radiation is delivered within the first 11 days. More than 10 million microspheres are deployed in each dose, and the targeted delivery minimizes damage to healthy liver tissue, Sirtex says.

- read the release
- here's more from The Sydney Morning Herald
- and more from Australia's FN Arena

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