WASHINGTON (AP) -- The Food and Drug Administration has approved the first drug made specifically to treat cancer in dogs.

Until now, all cancer drugs used in veterinary medicine were developed for use in humans and weren't specifically approved for animals. Federal law allows vets to administer cancer medicines and other human treatments under controlled circumstances.

The new drug, Palladia, manufactured by Pfizer Animal Health Inc., has been approved to treat a type of cancer that accounts for about one in five cases of canine skin tumors.

Canine cutaneous mast cell tumors -- the cancer in question -- can appear small and insignificant when dogs have them, but while some are easily removed, others can lead to life-threatening disease, according to the FDA.

"This cancer drug approval for dogs is an important step forward for veterinary medicine," Bernadette Dunham, director of FDA's center for veterinary medicine, said in a statement Wednesday.

"Prior to this approval, veterinarians had to rely on human oncology drugs, without knowledge of how safe or effective they would be for dogs," Dunham said. "Today's approval offers dog owners, in consultation with their veterinarian, an option for treatment of their dog's cancer."

Palladia is a tyrosine kinase inhibitor that works by killing tumor cells and cutting off blood supply to the tumor. Common side effects include diarrhea, decrease or loss of appetite, lameness, weight loss and blood in the stool.

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