Pathway Genomics, a company known for pushing the boundaries of direct-to-consumer genetic testing, on Thursday will launch a cancer screening test designed to detect bits of cancer DNA in the blood of otherwise healthy people.

The test represents a first in the rapidly developing field of "liquid biopsies," which use gene sequencing technology to screen blood samples for trace amounts of DNA associated with different cancers.

Several cancer diagnostic companies have been working on the tests, a field that has recently been joined by makers of DNA blood screening tests for fetal abnormalities after the tests detected early cancers in expectant mothers. Cowen & Co estimates that use of DNA blood tests for cancer screening will exceed $10 billion a year by the end of the decade.

But the move by Pathway, a privately owned maker of genetic tests ranging from cancer risk and heart health to drug response, underscores a growing debate over how much genetic information should be made available to healthy people if it is not yet clear how it can improve their health.

The company has already run into trouble on a similar issue. In 2010, Walgreens pulled Pathway's genetic testing kits from its pharmacies after U.S. health regulators warned patients might take action without understanding the results.

Several oncology experts said liquid biopsy tests like Pathway's, while exciting, still require large clinical studies proving they help people beat cancer through early detection. Doctors will also need a clear assessment of their accuracy.

"For any given test, the rate of false positives causing unnecessary alarm and false negatives that provide false security should be known," said Dr. Keith Stewart, an oncologist who heads Mayo Clinic's Center for Individualized Medicine.

Pathway's screening test looks at 96 genetic markers associated with major cancer types such as breast, ovarian, lung, colon and melanoma. The company is focusing on mutations that are relatively well-understood, and for which there are specific treatments, said Chief Executive Jim Plante.

The cost to consumers begins at $299 to periodically check for DNA in their blood that could act as an early warning sign of cancer. The tests must be ordered by a doctor, based on a patient's risk profile. A positive test will require additional checks to find where the cancer is growing.

Pathway also launched a blood test for patients already diagnosed with cancer to help determine whether a treatment is working, or whether the disease is likely to return.

SCREENING VS MONITORING

Scientists have long known that cancers shed bits of genetic material into the blood. Privately held Guardant Health and Personal Genome Diagnostics Inc already offer blood tests for cancer patients. Roche-backed Foundation Medicine Inc, Genomic Health Inc, Illumina Inc and Sequenom Inc say they have similar tests in the works.

But cancer experts say there are major differences between using such tests to screen for cancer and monitoring patients who are already known to have it.

For example, some early cancers may not secrete DNA fragments into the bloodstream and require other types of detection. A colonoscopy can find and remove polyps before they pose a threat as colon cancer.

"If we are relying on a test that can only detect cancer after it has formed, we miss a huge opportunity to intervene," said Dr. Scott Kopetz of the University of Texas MD Anderson Cancer Center.

Patients might be attracted to a less-invasive test for colon cancer, but if it is less effective, it might result in more cases of colon cancer, not fewer.

Another concern is that the tests may pick up on markers that are never destined to be cancer, something already known to occur in blood tests for prostate cancer, Kopetz said.

Pathway says its test is more than 99 percent accurate in detecting mutations in blood samples that contain at least nine copies of a tested mutation.

"We do expect to detect cancer DNA when the tumors are small - much sooner than stage three or four," Plante said.

Dr. Bert Vogelstein, a cancer geneticist at Johns Hopkins University in Baltimore, said Pathway's figure represents the test's technical ability to detect DNA in the blood.

Doctors, however, need an indication of how many patients will get a false positive result, something that can only be determined in a very large clinical trial, said Vogelstein. He is advising two companies developing liquid biopsy tests for cancer screening: Sysmex and Personal Genome Diagnostics.

Plante said the company has started two clinical trials involving patients but has yet to publish any results on how the tests perform in people.