The Food and Drug Administration is warning U.S. doctors about another counterfeit version of the cancer drug Avastin, the third case involving the best-selling Roche drug in the past year.

The FDA said in an online post Tuesday that at least one batch of the drug distributed by a New York company does not contain the active ingredient in real Avastin, which is used to treat cancers of the colon, lung, kidney and brain. The drug was distributed by Medical Device King, which also does business as Pharmalogical. The vials are packaged as Altuzan, the Turkish version of Avastin that is not approved for use in the U.S.

The agency warned doctors in April about a similar case of fake Turkish Avastin distributed by a U.K. distributor. Prior to that, the FDA announced in February an investigation into a different batch of fake Avastin distributed to doctors in several states. Both of those cases appeared to involve different networks of distributors than the latest incident.

The FDA said it's currently unclear whether any U.S. patients have received the drug. Specifically, Altuzan labeled with the lot numbers B6022B01 and B6024B01 may be counterfeit. Importing even authentic Altuzan into the U.S. is illegal, since the FDA has only reviewed Avastin as safe and effective.

The agency is asking doctors to stop using any products from Medical Device King, Pharmalogical or Taranis Medical, another affiliated business.

A telephone number listed on Medical Device King's website was not in service. Company representatives did not immediately respond to emails sent Wednesday.

Roche's Genentech unit sells Avastin in 120 countries and manufactures and packages the drug at eight sites worldwide. The drug had sales of $5.8 billion in 2012 and was Roche's second-best selling drug overall. The injectable drug usually sells for about $2,500 per vial.

The FDA warned doctors to be wary of drug prices that seem "too good to be true."

"Deep discounts may be offered because the product is stolen, counterfeit, substandard, or unapproved," the agency states.

Incidents of counterfeiting reported by drugmakers have increased steadily over the past decade, though only about 5 percent of cases are typically reported in the U.S. The rise in counterfeiting comes as pharmaceutical supply chains increasingly stretch across continents. More than 80 percent of the active ingredients used in U.S. pharmaceuticals are now manufactured overseas, according to a recent congressional report.