Governor Andrew Cuomo has signed a bill mandating broad insurance coverage for three-dimensional mammography, formally known as digital breast tomosynthesis, despite a lack of evidence about the long-term efficacy of the procedure.

The legislation—previously discussed here and here—fits a pattern of Albany writing coverage requirements into statute without careful, independent analysis of the costs and benefits.

Cuomo clarified in his approval memo, however, that the law “does not remove an insurer’s ability to review breast tomosynthesis for medical necessity.” This would leave plans at least some wiggle room to prevent overuse.

Tomosynthesis combines multiple X-ray images of a breast into a single three-dimensional composite. Though clinical studies show that technology is better at finding potential tumors, and less likely to result in false alarms, there is not yet long-term research to show whether it saves lives or otherwise improves outcomes. For this reason, the U.S. Preventive Services Task Force has declined to issue a recommendation either for or against the use of 3D mammography as a screening procedure for breast cancer.

The Cuomo administration previously issued regulatory guidance declaring that insurers must cover tomosynthesis “when medically necessary.” The bill sponsored by Assemblywoman Rebecca Seawright (D-Manhattan) and Senator Joe Griffo (R-Rome) appears to go further. It adds tomosynthesis to an existing mammography mandate that requires coverage for a “baseline” screening between 35 and 39, then annual screenings starting at age 40. It also makes no mention of medical necessity.

The New York Health Plan Association, which opposed the bill, raised concern that the more expensive 3D technology would “replace traditional mammography as the frontline screening for breast cancer” and contribute to rising healthcare costs.

However, if plans may still review the procedure for medical necessity—as Cuomo’s memo asserts—it’s not clear how much difference the new statute will make.

Also limiting the impact of the bill—as with all such state mandates—is the fact that it applies mainly to non-group and small-group policies. Most large employers are “self-insured” and thereby exempt under federal law. States also have no authority to regulate Medicare.

The Cuomo administration announced in August that 3D mammograms would be covered by the state’s Medicaid health plan for the poor and disabled.