A San Diego-based startup called Pathway Genomics released a blood test today that it says can detect mutations associated with multiple cancers. If true, the $699 test would be a big deal for medicine because it could be used to catch cancer before a person shows symptoms. But Pathway Genomics doesn’t have data that shows that the test actually works.

Pathway Genomics hasn’t finished the type of study that could be used to validate their claims — a fact the company acknowledges — so the company itself doesn’t know if its claims are true. And the FDA hasn’t reviewed the product, either. But that hasn't stopped it from marketing the test as a "cancer stethoscope."

"I am very reticent to believe a privately-funded personal genomics company’s claims when there is no peer-reviewed data to support their tests or technical approaches," says Isaac Garcia-Murillas, an oncologist at the Institute of Cancer Research in London who has been working on a blood test that may predict breast cancer relapse. He also doubts the test will find traces of tumor DNA in people who don’t have symptoms of cancer.

The test, called "CancerIntercept," detects cancer cell DNA in the blood. Pathway Genomics claims the test detects mutations associated with multiple cancers in people who are at high-risk for cancer, but who are "otherwise healthy." By this, Pathway Genomics means that these would-be cancer patients — the test looks for lung, breast, ovarian and colon cancers, as well as melanoma — haven’t yet shown symptoms. Another version of the test is meant to monitor the status of cancer patients. But the company’s marketing has largely focused on the technology’s ability to detect cancer at an early stage, an indication they have no evidence for.

"The sensitivity of the test is very high and it can be used to potentially catch cancers at a much earlier stage," says Jim Plante, CEO of Pathway Genomics. According to Plante, CancerIntercept has been validated through tests on "hundreds of samples."

That may be true, but the blood samples Pathway Genomics used for this validation came from patients with well-defined cancers, most of whom had advanced cancer, says Glenn Braunstein, Chief Medical Officer at Pathway Genomics. Detecting cancers in the blood of patients who are known to have cancer is decidedly not the same as detecting cancer mutations in people who haven’t yet been diagnosed.

Pathway Genomics also used the blood test on patients without cancer — but those tests weren't part of a long-term study to see if positive results led to a cancer diagnosis. In fact, Pathway Genomics hasn't completed that kind of study yet. "We are in the process of doing a longitudinal study," Braunstein says, adding that the company is currently performing follow-ups in "a number" of individuals. "We anticipate that [the study] will eventually make it in the peer reviewed literature."

Braustein himself told The Verge "a long term study" — exactly the type the company hasn’t done — "is the right way to determine what the clinical sensitivity is and what clinical specificity is." Instead, the company is relying heavily on previous studies, conducted using other tests in other labs.

When patients are monitored too closely, there’s a risk that they might be falsely diagnosed. In those instances, patients may seek medical assistance for a disease that never develops, or for a tumor that will never be serious enough to warrant treatment. A number of major preventative task forces, such as The American College of Physicians and American Urological Association, have moved away from early cancer testing recently because of this risk. But Pathway Genomics is heading head first into those waters.

Plante declined to comment on how the company managed to make a test that can accurately detect mutations in asymptomatic patients for a relatively low price.

No premarket FDA review

Most new health devices and drugs are reviewed by the US FDA before they hit the market, but that's not the case for CancerIntercept, which resides in an FDA blind spot. According to Plante, the test falls under the Clinical Laboratory Improvement Amendments as a "Laboratory Developed Test," defined by the FDA as tests that are designed, manufactured, and used within a single laboratory. The FDA doesn't generally enforce premarket review of these tests because they used to be "relatively simple lab tests and generally available on a limited basis," according to the agency's website.

But new technologies have changed that; LDTs have become more common and a lot more complex — and that means that there's a higher risk that faulty tests will make it to market. The FDA notified Congress last year that the agency would like to start reviewing LDTs before they’re sold, but changing that regulation could take years. So, whether the FDA does anything about Pathway Genomics' CancerIntercept test will depend on how the startup markets its product, and what kinds of claims they make about what the test detects. The Verge got in touch with the FDA to verify Pathway Genomics' claims, but an FDA spokesperson said that she couldn't comment on the test.

So Pathway Genomics is launching the test today; would-be customers can apply for the test online. Then, their applications are reviewed by a telemedicine physician. Or patients can request the test through their doctors. On the phone, Braustein said that he didn't know exactly how many people had taken the test so far, and he declined to state how many healthy individuals had received positive tests results.

Our knowledge of cancer mutations and the role they play in diagnosis is still in its infancy. That means tests like Pathway Genomics’ blood test are on shaky scientific ground. Right now, the research scientists need to determine if this blood test is any good doesn't appear to exist. And the FDA isn’t able to regulate the test. Our diagnosis? Caveat emptor.