Biotech Stock Mailbag: Exact Sciences, Galena, Titan, Arena, Breakthrough Therapy

BOSTON ( TheStreet) -- Welcome to this week's Biotech Stock Mailbag.

Steven D. writes, "I have been long Exact Sciences ( EXAS) for a number of years waiting for their pivotal study to read out. Any idea on the timing of the study and views from the short side of the trade?"

Top-line results from Exact Sciences' pivotal "Deep-C" study of Cologuard are expected before the end of April. Steven is right, the wait has been long, so let's go over the study design and talk about expectations.

The Deep-C study evaluates Cologuard as a new, non-invasive screening test for colon cancer and pre-cancerous lesions. Cologuard isolates and identifies cancerous and pre-cancerous DNA from a patient's stool sample. Exact Sciences designed Cologuard to more accurately detect early stage colon cancer and pre-cancerous lesions compared to the existing stool-based screens FOBT and FIT, which can pick up 40-60% of colon cancers and are even less accurate in detecting pre-cancerous lesions.

Cologuard isn't necessarily designed to be more sensitive than a colonoscopy, but Exact Sciences argues that adoption of the non-invasive and easy-to-use Cologuard will lead to higher colon cancer screening rates. (Half of Americans recommended for colon exams choose not to be tested.) Used ahead of colonoscopy, Cologuard could also improve the detection of pre-cancer and early stage cancer when it is most treatable and curable.

More than 10,000 patients at average risk for colon cancer were enrolled in the Deep-C study. Each patient in the study receives a colonoscopy while a sample of their stool is also tested with Cologuard and a FIT test. The study's primary endpoint compares the sensitivity and specificity of Cologuard to colonoscopy. Secondary endpoints will compare Cologuard to colonoscopy in the detection of pre-cancerous lesions, and non-inferiority between Cologuard and FIT.

The target performance for Cologuard is 85% sensitivity and 90% specificity.

Are these targets achievable? Yes, easily, given the available screening data already presented. Exact Sciences has conducted three validation studies of Cologuard overall. The last two studies conducted in 2011 and 2012 were the most relevant and yielded colon cancer sensitivity rates of 98% each time. Importantly, sensitivity rates for stage 1 and 2 colon cancers were just as high. For pre-cancerous lesions, the sensitivity rates were 59% and 57%, respectively.

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