LOS ANGELES — Celgene Corp. has agreed to pay $280 million to settle a whistle-blower lawsuit alleging the pharmaceutical company committed fraud promoting a drug with a notorious history that was repurposed to treat leprosy and another therapy for unapproved cancer treatments, federal prosecutors announced Tuesday.

The agreement settled a lawsuit in Los Angeles federal court by a former Celgene saleswoman who said the New Jersey-based company submitted false claims to Medicare and health care programs in 28 states and Washington, D.C., which were all parties to the settlement.

“Patients deserve to know their doctors are prescribing drugs that are likely to provide effective treatment, rather than drugs marketed aggressively by pharmaceutical companies,” said Acting U.S. Attorney Sandra R. Brown.

The lawsuit filed by Beverly Brown was brought on behalf of the U.S. government under a federal whistle-blower law. She could receive as much as $84 million in the settlement.

Celgene denied wrongdoing.

Brown was an “immunology specialist” trained by Celgene to promote Thalomid and Revlimid drugs for cancer treatments, the lawsuit said.

Thalomid, another name for thalidomide, a drug prescribed for morning sickness in the 1950s and 1960s that caused severe birth defects, was approved by the agency in 1998 for treating leprosy.

Because Thalomid would only be useful to a fraction of the few hundred leprosy cases diagnosed in the U.S. each year, the company developed a plan to promote the drug for cancer, the lawsuit said.

Doctors can prescribe drugs for other purposes if they think they will be effective, and the company marketed the drug directly to them to treat blood cancers and tumors, the lawsuit said.

The FDA contacted Celgene and sent letters warning about its promotional efforts and for failing to warn about potential fatal risks from the toxic drugs, the lawsuit said.

“Their use in off-label indications was tantamount to human experimentation,” Brown’s lawyers wrote in one court filing. “Celgene compounded this by instructing its sales representatives to conceal the drugs’ risks, including most notably the potential for lethal blood clots.”

While Thalomid and Revlimid, a successor derived from thalidomide, were later approved for limited cancer treatments, their widespread promotion in advance of approvals led Celgene to become the company it is today, the lawsuit said.