TIL therapy shrank tumors in about a third of patients who had run out of treatment options, according to a clinical trial.

The Food and Drug Administration on Friday approved a new cancer therapy that could one day transform the way a majority of aggressive and advanced tumors are treated.

The treatment, called Amtagvi, from Iovance Biotherapeutics, is for metastatic melanoma patients who have already tried and failed other drugs. It’s known as TIL therapy and involves boosting the number of immune cells inside tumors, harnessing their power to fight the cancer.

It’s the first time a cellular therapy has been approved to treat solid tumors. The drug was given a fast-track approval based on the results of a phase 2 clinical trial. The company is conducting a larger phase 3 trial to confirm the treatment’s benefits. The therapy’s list price — the price before insurance and other potential discounts — is $515,000 per patient.