A tray containing cancer cells sits on an optical microscope in the Nanomedicine Lab at UCL's School of Pharmacy in London. REUTERS/Suzanne Plunkett The FDA on Wednesday approved a new kind of drug to treat the most common form of bladder cancer.

The drug, which goes by the name Tecentriq and was developed by Genentech, is a cancer immunotherapy. Unlike chemotherapy, which involves administering powerful drugs that kill both cancerous and healthy cells (most healthy cells can repair themselves), immunotherapies harness the power of the immune system to help it identify and knock out just the cancerous cells.

It's part of a class of drugs called PD-L1 inhibitors that help the immune system fight cancer by essentially, it helps the immune system take its foot off the brakes and go after the tumor cells. Similar drugs that take the same approach include Keytruda, made by Merck, and Opdivo, which is made by Bristol-Myers Squibb.

This is the first approval in this class of drugs for this type of cancer, the FDA said in a release.

The drug will treat urothelial carcinoma, which occurs in the urinary tract system, involving the bladder and related organs. It is designed for patients whose cancer has progressed despite platinum-based chemotherapy and may have limited treatment options. This is just the first of many types of cancer that Tecentriq is being studied to treat.

Roche, the Swiss drugmaker that owns Genentech, is banking on the drug to bring in billions in revenue by 2020 as a centerpiece of its strategy to counter the threat of biosimilar versions of its older medicines.

(Reuters reporting by Natalie Grover in Bengaluru)