The preliminary results of the long-awaited SIRFLOX study were released over a month ago, leading to very negative reactions. Shares dropped down nearly 55%, losing Sirtex nearly $1 billion in the process! Was this reaction justified or have investors acted prematurely?

The SIRFLOX study found that Sirtex Medical's SIR-Spheres, when added to a first-line systemic chemotherapy regimen for the treatment of non-resectable metastatic colorectal cancer (mCRC), did not show any statistically significant improvement in overall progression-free survival. Overall progression-free survival measures the length of time that lapses before existing tumors start to progress and/or before new tumors develop in any organ. However, the SIRFLOX study did show statistically significant improvement in progression-free survival in the liver. Sirtex reports that up to 90% of mCRC patients die of liver failure as liver tumors are the only, or dominant, site of disease in patients with mCRC.

If this is the case, then why is the study still considered to negatively impact the SIR-Spheres? Why have all those investors sold their shares? Through speaking with an interventional oncologist I learned that while the liver is the dominant site for colorectal cancer metastases, it is rare that it is the only site. A significant number of the mCRCs will metastasize to the lungs and elsewhere, leading to cancer in multiple sites. This leaves just a fraction of patients with mCRC that would be suitable for SIRT, with some considering it to be a niche product. While the stock had dropped to as low as $17.53 a share, it has grown over the course of the month up to $23.13 a share still far away from its value of $39 a share before the results were released. Many investors do acknowledge that the share price fall was an overreaction and believe that the results should not change anything going forward.

Although the preliminary results have been released for some time, the final results will be submitted to the American Society of Clinical Oncology (ASCO) Annual Meeting, which will be held from May 29 , June 2nd 2015 in Chicago, Illinois. Given that the primary endpoint is not likely to support the use of SIR-Spheres, any adverse results for the secondary endpoint would definitely shock the market.

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