By Liz Essley Whyte

If your cancer lab test isn’t valid, wrong results could mean you don’t get a drug that could save your life. Or it could mean you take a drug that won’t help you but will bombard you with side effects.

Lab tests influence nearly two-thirds of medical decisions, including high-stakes ones such as choosing treatments for cancer or diagnosing a genetic disorder in a newborn. As medicine has advanced, labs have seen an opportunity to offer more tests, and now lead a $10 billion industry that, so far, has advanced with little scrutiny from the Food and Drug Administration.

That’s changing.

The agency on Monday issued a final rule detailing how it will oversee the labs that offer tests for things as diverse as illicit drugs and genetic indicators for disease risk. The rule is set to go into effect in about two months.

The agency will first scrutinize, under the rule, tests that are complicated or high-stakes. That could include tests that can determine what specific subtype of cancer you have and whether you would respond to specific drugs. If those tests are wrong, you could be taking drugs with devastating side effects that don’t work as well against your cancer, or not getting drugs that could have cured you.

Lab-developed tests, designed and conducted within a single laboratory, boomed in the past two decades and now make up about half of all lab tests, estimates Grand View Research. For many years the FDA allowed hospitals and other groups to conduct the tests without agency oversight, but now the FDA wants labs to prove they are accurate.

“The agency cannot stand by while Americans continue to rely on results of these tests without assurance that they work,” said FDA Commissioner Robert Califf. “The final rule announced today aims to provide crucial oversight of these tests.”

The rule is likely to reshape how such medical testing is done in the U.S. The FDA has said inaccurate tests marketed in recent years could have led to patients getting the wrong treatments for heart disease or cancer, or being incorrectly diagnosed with rare diseases, autism and Alzheimer’s disease.

“I don’t want tests out there that we don’t know anything about and might not even work,” said Dr. Daniel Hayes, a University of Michigan cancer researcher who has pushed for more oversight of lab-developed tests for cancer types.

The industry had argued that it is already regulated by federal rules governing laboratories and that further oversight would discourage innovation and increase wait times for results. The final rule exempts certain tests that were already on the market from some oversight—a provision that industry groups had pushed for.

Critics of the rule have also said the FDA is reaching past its legal authority.

“The FDA does not have the authority to unilaterally increase its regulatory jurisdiction,” said Sen. Bill Cassidy, the Louisiana doctor who leads the Republican wing of the Senate’s health committee. “This rule will undermine access to essential laboratory tests, increase healthcare costs and ultimately harm patients.”

The FDA has been pushing to regulate lab-developed tests for years, but earlier efforts to regulate or get Congress to legislate on the matter fizzled.