“We recognize that most payers in the U.S. are not currently set up to support one-time therapies that generate long-term transformative benefits,” Ms. Pingpank said.

Indeed, health care executives already are rushing to develop new payment models.

When Kymriah was approved, officials at Novartis said they would take the unusual step of taking into account how well it worked in a particular patient.

The company said it was collaborating with the federal Centers for Medicare and Medicaid Services on an approach in which, for children and young adults, there would be no charge if the patient did not respond to the treatment within a month.

If, as expected, Kymriah is approved for other blood cancers, its price may vary depending on how effective it is for those diseases.

Express Scripts, a pharmacy benefit manager that contracts with insurance companies to provide medications to patients, has taken up the cost question with gene therapy companies, insurers and the federal government.

“It’s amazing how many think this is in the future,” said Dr. Steve Miller, chief medical officer at Express Scripts, said of the looming payment problem. “This is right now.”

The idea favored by Dr. Miller and others is to pay for these novel drugs as you might a mortgage on a house.