Updated with new information.

MADISON, Wisc. ( TheStreet) -- Exact Sciences ( EXAS - Get Report) is trading lower Thursday on results from a pivotal study of its non-invasive colon cancer screening test. Cologuard's accuracy met the endpoints of the pivotal study but not enough to satisfy investors.

Shares of Exact are down 31% to $6.84 in Thursday pre-market trading.

In the study of 10,000 patients at average risk for colon cancer, Cologuard demonstrated 92% sensitivity for the detection of colon cancer and 42% sensitivity for the detection of pre-cancerous lesions. The test achieved a specificity of 87% during the trial, Exact Science said.

Based on these results, Exact Sciences will seek U.S. approval of Cologuard as a new screening test for colon cancer later this year.

Investors, however, were hoping for better accuracy from Cologuard based on prior study results. In particular, the 42% sensitivity for pre-cancerous lesions fell way short of Cologuard's earlier studies in which sensitivities for pre-cancer were in the high 50% to low 60% range. Detection and removal of pre-cancerous lesions can significantly reduce the incidence of colon cancer, similar to what happened to cervical cancer following the introduction of pap smear tests.

On a conference call with investors, Exact Sciences CEO Kevin Conroy acknowledged that Cologuard's ability to detect pre-cancerous lesion fell below the company's expectations but he insisted that the screening test would still be viewed as effective by doctors and insurers.

"We believe these data are powerful," said Conroy.

Investors were also hoping to see specificity closer to 90%; the actual 87% result is seen not coming close enough. Specificity measures the test's ability to accurately detect a negative result. In this case, however, for every 100 patients who don't have cancer or pre-cancerous lesions, Cologuard will come back reading a positive cancer signal. A false-positive rate this high could prove problematic for Exact Sciences, particularly as it tries to market the test to doctors who treat patients at low risk for disease.

Cologuard is a 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 but are less accurate in detecting pre-cancerous lesions.

Cologuard isn't necessarily designed to be more accurate than a colonoscopy, but the company believes 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.

-- Reported by Adam Feuerstein in Boston.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.