Cancer patients or their families often arrive at oncologists’ offices holding printouts about genetic tests that they found on the Internet.

The tests promise profound results: By understanding the genetic makeup of a patient — or a tumor — doctors will then be able to tailor the best treatment for that individual patient. President Obama just proposed a $215 million investment in the 2016 federal budget for this new medical frontier, known as personalized or precision medicine.

But a study published recently in the Journal of the National Cancer Institute led by two Dana-Farber Cancer Institute doctors shows that the promise is still just that: The vast majority of websites offering genetic tests over-emphasize potential benefits, fail to disclose significant limitations and may not be useful in guiding cancer treatment.

“While valuable cancer tests and services are marketed over the Internet, there are also many tests that are marketed online that may not be helpful,’’ said Dr. Stacy Gray, one of the study’s lead authors, of the Center for Population Sciences, Department of Medical Oncology at Dana-Farber. “Patients and providers need to critically evaluate what they see online.”

Gray — along with fellow lead author Katherine Janeway, a pediatric oncologist at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center, and other researchers — identified 55 websites that offer a broad range of tests and services.

The study catalogued each website based on what tests were offered, the quality of information and other factors. Then, an expert panel reviewed the tests — coming to the conclusion that 88 percent of the websites offered one or more tests that lacked evidence that they benefited patients.

The doctors noted that precision medicine has great potential but patients and doctors need to carefully evaluate testing claims. The tests are not regulated by the U.S. Food and Drug Administration and, as a result, companies offering them escape any requirement they must prove tests do what they promise.

"If a personalized cancer medicine test or service provides information about a patient's diagnosis, prognosis or treatment options, it may improve the patient's chances of cure," Janeway said in an email interview with the New England Center for Investigative Reporting. “But proving that a personalized medical test or service improves cure rates requires appropriately designed research studies."

Janeway said the biggest surprise about the findings was how few websites gave information about the cost of tests and what insurance would cover. About only half of the commercial websites included the cost of testing, which ranges between $99 and $13,000. Some websites said insurance would cover the tests, while others were vague or did not mention prices.

Gray said while she expected the websites to include less information about a test's limitations than its benefits, "it was striking how rarely websites mentioned important limitations such as the possibility of getting a false positive test result or the complexity of interpreting genomic data."

The researchers are now taking the question a step further, looking at cancer genomic tests and treatments reported in the media to see if there is hype over unproven tests and treatments.

The New England Center for Investigative Reporting is an independent, nonprofit newsroom based out of Boston University and WGBH News.