By Manojna Maddipatla and Manas Mishra

The U.S. Food and Drug Administration on Wednesday approved Karyopharm Therapeutics Inc's treatment for multiple myeloma, a type of blood cancer.

The drug Xpovio was approved in combination with dexamethasone for patients who have received at least four prior therapies and who fail to respond to certain other treatments, the agency said.

"Sadly, often over time, patients can exhaust all available treatments and still see their disease progress," said Richard Pazdur, director of the FDA's Oncology Center of Excellence.

Karyopharm said it expects Xpovio to become commercially available in the United States by July 10.

The drug, chemically known as selinexor, binds to and inhibits a protein called XPO1, leading to the accumulation of cancer-suppressing proteins in the cells.

The U.S. health regulator was to initially decide on the treatment's approval in April, but pushed back the date by three months to review additional data submitted by the company.

Multiple myeloma is estimated to cause nearly 13,000 deaths in the United States in 2019, according to the American Cancer Society.

Shares of the company closed down 36% on Wednesday.