MADISON, Wisc. ( TheStreet) -- Exact Sciences ( EXAS) is enrolling patients in a large late-stage study of its colon cancer-screening test Cologuard to support a planned U.S. approval filing, the company announced Tuesday.

Cologuard is designed to detect altered genetic material in cells that are shed from the lining of the colon into stool from pre-cancerous and cancerous lesions. The Exact Sciences test can also detect blood in stool, which is another possible signal of colon cancer.

Patients benefit most when cancer is detected as early as possible, which is why Exact Sciences is engineering Cologuard to be especially sensitive to pre-cancerous lesions in the colon. Existing colon-cancer screening tests don't do a good job of picking up early-stage cancer.

The Cologuard phase III study began enrolling patients at the end of June and will recruit more than 10,000 patients between the ages of 50 and 84 who are at an average risk for colon cancer. All the patients will have stool collected for a Cologuard test and a commercially available fecal blood test. The patients will then undergo a standard colonoscopy. Doctors and patients will not be told the results of the Cologuard and fecal blood tests, which at the end of the study will be compared for accuracy against the results from the colonoscopy. Lesions suspected of being cancer will be confirmed by independent laboratory examination.

Exact Sciences says enrolling patients in the phase III colon cancer screening study will take between 12-15 months. Recruiting well over 10,000 patients may be necessary if the incidence of colon cancer detected in the study population is lower than predicted, said an Exact Sciences spokesperson.

Cologuard detected 85% of colon cancers and 64% of early pre-cancers, according to a validation study presented last year. The pre-cancer sensitivity, in particular, was especially strong, surpassing the company's goal of detecting 50% of pre-cancerous lesions.

Exact Sciences shares closed Monday at $8.80. The stock has more than doubled in value over the past year.

Colon cancer is the second leading cancer killer in the U.S, with about 142,000 new cases and 51,000 deaths each year, according to the National Cancer Institute. The American Cancer Society recommends that all Americans start getting tested for colon cancer at age 50. However, many patients do not comply fully with current screening recommendations. In fact, 60% of patients today are diagnosed with colorectal cancer in the late stages, primarily because of poor screening compliance.

--Written by Adam Feuerstein in Boston.

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