(Reuters) – The U.S. Food and Drug Administration said on Wednesday it approved Merck & Co Inc’s Keytruda for a hard-to-treat form of bladder cancer, making it the first new treatment for the cancer in more than two decades.

The therapy was approved for patients with a high-risk, non-muscle-invasive bladder cancer who have undergone prior treatment and are ineligible for or have opted out of surgical removal of the bladder.

The approval was based on results from a mid-stage study in which nearly 41% of patients on Keytruda showed a complete response, with about half of them having a complete response for at least a year.

“This is the first time that we’re recognizing that systemic immune activation can lead to durable remission of cancer,” said Dr. Arjun Balar of NYU Langone’s Perlmutter Cancer Center, the study’s lead investigator.

“That is probably the path forward in terms of helping our patients preserve their bladder with bladder cancer.”

Non-muscle-invasive bladder cancer is commonly treated with the Bacillus Calmette-Guerin vaccine. However, patients who do not respond to the vaccine have limited treatment options other than surgery, which comes with substantial risk of complications, hospitalizations, and even death.

Merck had estimated that more than 80,000 Americans were newly diagnosed with bladder cancer over the last year, of which more than three fourths of patients were expected to have non-muscle-invasive bladder cancer.

Keytruda is already approved for treating a number of cancers including melanoma, lung cancer, head and neck cancer and Hodgkin lymphoma.

(Reporting by Saumya Sibi Joseph in Bengaluru; Editing by Aditya Soni)