CHICAGO (CBS) — The FDA is warning doctors across the country, including a facility in Chicago, about counterfeit vials of the cancer drug Avastin.

As CBS 2’s Suzanne Le Mignot reports, Dr. R. Deva Nathan, of the Cancer Treatment Center, said he never used Avastin from the company in question and never received a shipment, so none of his patients ever received the counterfeit version of the medication.

Nathan said he believes he received the FDA warning letter due to past purchases from one of the companies in question.

The words on legitimate boxes of Avastin are written in English. The company name, Genentech, is visible on the lower left corner of the box. The bottle clearly shows the word Avastin across the center of the label.

The fake version’s box is written in French, with the manufacturer labeled as Roche, and the expiration and lot number on the front of the bottle, instead of the side, like the real Avastin.

The intravenous medication is used to shrink cancerous tumors.

Dr. Howard L. Kaufman, director of the Rush University Cancer Center, said it’s frightening to think that cancer patients could be getting treatment with something that won’t shrink their tumors like Avastin does.

“I think it’s why it’s very important that patients who are dealing with cancer go to a reputable institution,” Kaufman said.

Kaufman said Rush has extra precautions in place to guard against any counterfeit drugs infiltrating their cancer-fighting drug supply. Genentech, the company that manufacturers Avastin, is asking pharmacists to be vigilant, and to be on the lookout for the lot numbers that are in question.

“I think the lesson is that we have to be very careful and look at the label very carefully,” Kaufman said. “This is like finding counterfeit money. Sometimes it may be very obvious, but if you’re not looking … you can certainly miss it.”

One 400 milligram vial of Avastin can cost around $2,000.

The FDA sent letters to 19 medical centers that purchased medications from a foreign supplier. The majority are in southern California. Two are in Texas and one is in Chicago.

The physician with the Chicago office said he received the FDA warning letter because of past purchases from one of the companies in question. He stressed he never used or purchased Avastin from that company.