Senate finance Committee members Elizabeth Warren (D-MA) and Bill Cassidy (R-LA) are pushing to have a hearing to discuss the Medicare coverage of Aduhelm (aducanumab), Biogen’s controversial Alzheimer’s treatment, which recently won FDA approval.

In a letter addressed to Senate Finance chair Ron Wyden (D-OR) and ranking member Mike Crapo (R-ID), Warren and Cassidy express concern that the drug could cost Medicare $37 billion to $90 billion annually. “This level of potential new spending, particularly for just one product with limited evidence of clinical efficacy thus far, tests the program’s resiliency,” they wrote.

The letter also recommends that Medicare consider limiting the use of the drug to patients most likely to benefit from it. The clinical trials for aducanumab focused on Alzheimer’s patients with mild cognitive impairment.

Biogen has yet to provide rigorous clinical evidence to tie the drug to improved cognitive performance in Alzheimer’s patients. FDA approved the drug based on a surrogate endpoint  — namely, reduction of amyloid beta plaques in the brain.

Warren and Cassidy also hint that Congress reform Medicare spending to be “value-based,” linking prescription drug pricing to clinical effectiveness. The two also entertain the possibility that Medicare could refuse coverage of the drug.

The senators are concerned that up to six million Alzheimer’s patients in the U.S. could use the drug in perpetuity. The list price of the drug is $56,000.

FDA could technically rescind approval if the drug does not yield a verifiable clinical benefit in a Phase 4 study.