The U.S. Food and Drug Administration has expanded the authorized use of Celgene Corp's cancer drug Revlimid to include newly diagnosed patients with multiple myeloma, the company said on Wednesday.

Previously the drug was only approved for patients who had received at least one previous therapy. Physicians in the United States have long been prescribing Revlimid for new patients on an "off-label" basis, but the company had not been allowed to promote its use in this population.

The FDA's action means Celgene can market Revlimid, in combination with a different drug, dexamethasone, as a treatment for all multiple myeloma patients and helps validate the company's premise that treating patients earlier and for a longer period of time increases progression-free survival.

The approval is expected to only modestly increase sales in the United States since doctors are already prescribing the drug for newly diagnosed patients.

In Europe, where physicians are not allowed to prescribe off-label, the situation is different. Celgene expects European regulators to also approve the drug for newly-diagnosed patients within the next few weeks. If they do, the move could add meaningfully to sales.

About 50 percent of patients with multiple myeloma are newly diagnosed. The remainder have received one or more prior therapies.

Revlimid generated total sales in 2014 of $2.92 billion in the United States and $2.06 billion in the rest of the world. The drug is approved in 70 countries for previously treated patients. The company hopes approvals in the U.S. and Europe will pave the way for other countries to also approve the drug for newly diagnosed patients.

John Newman, an analyst at Canaccord Genuity, said in a research note that he expects sales of Revlimid to reach $10 billion by 2020.

About 93,600 patients are living with multiple myeloma in Europe and about 88,499 patients are living with it in the United States, Celgene said.

Revlimid is also approved in the United States and some other countries for a group of blood disorders known as myelodysplastic syndromes. It is also approved in the United States for patients with mantle cell lymphoma whose disease has progressed after two prior therapies.

Celgene's shares were up 1.4 percent to $117.96 in Wednesday morning trade on Nasdaq.