Cancer cells are seen on a large screen connected to a microscope. Reuters

The US Food and Drug Administration just approved a cutting-edge cancer therapy.

On Wednesday, the FDA approved Novartis' Kymriah, also known as tisagenlecleucel, a treatment for pediatric acute lymphoblastic leukemia.

"I think this is the most exciting thing I've seen in my lifetime," said Dr. Tim Cripe, an oncologist who was part of the FDA advisory committee panel that voted in July to recommend the drug's approval.

The highly personalized treatment is called CAR T-cell therapy (CAR is short for chimeric antigen receptor). It's a type of cancer immunotherapy, which harnesses the body's immune system to take on cancer cells. It removes a person's cells, reengineers them, then puts them back in their body to attack cancer cells.

"We're entering a new frontier in medical innovation with the ability to reprogram a patient's own cells to attack a deadly cancer," the FDA commissioner, Scott Gottlieb, said in a statement. "New technologies such as gene and cell therapies hold out the potential to transform medicine and create an inflection point in our ability to treat and even cure many intractable illnesses. At the FDA, we're committed to helping expedite the development and review of groundbreaking treatments that have the potential to be life-saving."

The one-time treatments won't come cheap — Novartis said it would cost $475,000, though it also said in a news release Wednesday that it was working with the Centers for Medicare and Medicaid Services to come up with a payment system that reflects how well the drug works in a person. As part of the collaboration, CMS will have to pay "only when pediatric and young adult [acute lymphoblastic leukemia] patients respond to Kymriah by the end of the first month," Novartis said.

Novartis' therapy is one of two cutting-edge treatments for blood cancers that are poised to get approved by the end of the year.

The FDA is also expected to make a decision about another CAR-T therapy, from Kite Pharma, which just got acquired by Gilead Sciences, for aggressive B-cell non-Hodgkin lymphoma. Kite said in February that of the 101 patients in its trial, 36% had a complete response to the treatment (meaning the cancer had disappeared) after six months.

It's a type of cancer that Novartis also wants to get approval to treat. In June, Novartis released data from its Phase 2 trial of tisagenlecleucel in adult patients with diffuse large B-cell lymphoma, an aggressive form of lymphoma. Of the 51 patients in the trial, 23 had either a complete response or a partial response (meaning their tumor displayed signs of shrinking).

New treatments like Kymriah face some other challenges: