U.S. regulators have approved a first-of-a-kind test that looks for mutations in hundreds of cancer genes at once, giving a more complete picture of what's driving a patient's tumor and aiding efforts to match treatments to those flaws.

The U.S. Food and Drug Administration approved Foundation Medicine's test for patients with advanced or widely spread cancers, and the Centers for Medicare and Medicaid Services proposed covering it.

The dual decisions, announced late Thursday, will make tumor-gene profiling available to far more cancer patients than the few who get it now, and lead more insure...