MADISON, Wis. (TheStreet) -- An independent panel of health care experts didn't include Exact Sciences' (EXAS) - Get Exact Sciences Corporation Report Cologuard on a draft list of recommended colon cancer screening tests in the U.S.

The disappointing Cologuard review caused Exact Sciences' shares to slide 43% Tuesday to a two-year low on fears that the Madison, Wis.-based company will find it more difficult to win favorable reimbursement from private insurers.

Exact Sciences CEO Kevin Conroy, speaking on a Tuesday morning conference call, said the decision by the U.S. Preventive Services Task Force to omit Cologuard from its draft list of recommended colon cancer screening tests was "different from what we and most people expected."

Cologuard was included on USPSTF's list of "alternative" colon cancer screening options, although how it should be used was not defined in the draft proposal.

USPSTF recommendations are not binding and sometimes controversial -- as was the case last year with changes made to prostate cancer screening guidelines -- so it's not clear if interest in Cologuard from doctors and private insurers will be diminished.

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On Tuesday's call, Conroy said there's "no reason to believe the task force will impact the strong Cologuard launch," referring to the USPSTF draft recommendations. The company intends to lobby USPSTF to include Cologuard on its recommended list for colon cancer screening tests before the draft report becomes finalized later this year.

Cologuard is a colon cancer screening test which works by detecting genetic mutations found in stool samples. Exact Sciences secured FDA approval for Cologuard based on a large study that found the test highly sensitive to detecting early-stage colon cancer as well as precancerous lesions. This is important because colon cancer, when detected early, is highly curable.

Exact Sciences launched Cologuard last year with an important endorsement and favorable pricing reimbursement from the Centers for Medicare & Medicare Services, the government agency which runs the Medicare and Medicaid healthcare programs.

In the draft report issued Tuesday night, USPSTF acknowledged that Cologuard (referred to as FIT-DNA) was more sensitive than older, stool-based colon cancer screening methods, but might also cause more false positive results, thereby causing more confirmatory colonoscopies to be performed. The panel also faulted Cologuard for lacking studies assessing the impact on use with cancer incidence, quality of life and mortality.

In early Tuesday trading, Exact Sciences shares had fallen to $10.52. Analysts expect Exact Sciences to deliver $43 million in Cologuard revenue this year and $140 million in 2016.

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.