A man walks past Pfizer's world headquarters in New York April 28, 2014. REUTERS/Andrew Kelly/File Photo

(Reuters) - The U.S. Food and Drug Administration (FDA) said on Thursday it approved Pfizer Inc’s rare blood cancer drug, Besponsa, with a boxed warning.

Besponsa was approved to treat adults with relapsed or refractory B-cell precursor acute lymphoblastic leukemia (ALL).

Based on the typical duration of treatment, the total cost of the drug will be $168,300, before discounts to purchasers, Pfizer told Reuters.

The list price of a drug is not necessarily what patients actually pay. ‘Out-of-pocket’ costs vary based on duration of the treatment and individual healthcare plans.

Besponsa will carry a boxed warning, the severest form of warning by the FDA, saying patients treated with the drug were at a risk of severe liver damage as well as an increased risk of death for patients who take the drug after receiving a certain type of stem cell transplant.

B-cell precursor ALL is a rapidly progressing cancer in which the bone marrow makes too many B-cell lymphocytes, an immature type of white blood cell.

Besposa — approved in the European Union earlier this year — is a targeted therapy that binds to B-cell ALL cancer cells that express the CD22 antigen, blocking the growth of cancer cells.

According to the National Cancer Institute, ALL will affect about 5,970 people in the United States this year and kill about 1,440. (bit.ly/2uUrKu8)

Pfizer shares were down about 1 percent at $33 on Thursday.