Wednesday was a historic day in the biotech field.

A revolutionary way of fighting cancer was approved for the first time by the Food and Drug Administration.

Novartis’ (NYSE: NVS) CAR-T therapy Kymriah got the green light from U.S. regulators to treat children and young adults with B-cell acute lymphoblastic leukemia who aren’t responding to other more conventional treatments.

These patients will most likely die without the drug.

CAR-T (or chimeric antigen receptor T-cell) therapy harvests a patient’s white blood cells. The cells are re-engineered to fight the cancer and then injected back into the body.

In Kymriah’s clinical trials, a staggering 83% of patients were cancer-free three months after receiving a single treatment.

Most cancer drugs are considered “successful” if 25% or more patients respond to treatment.

Kymriah will be expensive. The price tag is $475,000 – but in a break from tradition, the patient will be charged only if the treatment works. If a patient doesn’t respond to the treatment within one month, they (or their insurance company) will not be billed.

There are dangers with CAR-T therapies. Most patients experience very high fevers or severe flu-like symptoms, and a few patients have died in clinical trials.

But patients who come out on the other side have a great chance of beating their cancers.

There are other companies with CAR-T drugs, including Kite Pharma (Nasdaq: KITE), that agreed to be acquired by Gilead Sciences (Nasdaq: GILD) last week.

So far, CAR-T drugs have been shown to work in blood cancers only. They have not yet been effective with solid tumors.

Nevertheless, it is the most exciting thing to happen in cancer therapy in decades. It is not an exaggeration to say that it will likely save thousands of lives in the coming years.

Amazingly, CAR-T therapy might not even be the biggest breakthrough in medicine this decade.