One of the world's most successful drugs, Merck's (NYSE:MRK) Keytruda, stands to become even more prominent following an important new approval. The U.S. Food and Drug Administration (FDA) gave it the green light for the treatment of a particularly stubborn type of bladder cancer.

The FDA's approval covers high-risk, non-muscle-invasive bladder cancer that has not responded to the Bacillus Calmette-Guerin vaccine. The approval is not broad; it applies only to patients who have already received other forms of treatment, and cannot or are unwilling to have their bladders surgically removed.

Cancer attacking an organism

Image source: Getty Images.

Nevertheless, it is certain to be in demand for such treatments. Merck acknowledged this in its press release announcing the approval, saying that Keytruda "will be a new clinical option for a patient population that previously had limited FDA-approved therapies available."

Keytruda already has a set of FDA approvals covering other forms of cancer, including those that attack the skin and lungs. It is an immunotherapy treatment, meaning that it mobilizes the body's immune system to identify and eliminate cancer cells. 

Keytruda received its first green light from the regulator in 2014. Over the past few years, its popularity has rocketed higher. In Merck's most recently reported quarter, sales of the drug rose by 62% on a year-over-year basis. The revenue from Keytruda alone was $3.1 billion -- nearly 25% of the company's total top line for the period.

In spite of the FDA's nod, the price of the high-profile pharmaceutical stock did not move significantly on Wednesday. Merck's shares closed slightly lower on the day.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.