Bevacizumab (Avastin) is a revolutionary drug. A monoclonal antibody against a protein called vascular endothelial growth factor, it blocks the formation of blood vessels that feed the cancer—and is the first drug of this kind approved for use in the U.S.

Over the past eight years, Avastin has become popular for use against metastatic colon cancer, lung cancer, and recurrent brain cancer. Its effectiveness against advanced breast cancer is controversial.

But few would say that Avastin isn’t highly useful, despite such side effects as fatigue, vomiting, and blood clots. It is also expensive, with a yearly course costing about $100,000. However, there is no current shortage of it like there is for several other common chemotherapies due to excess regulation, sterilization procedures, and shrinking profit margins as drugs go generic.

Avastin faces another problem. Counterfeiters make a drug without its main active ingredient. Not only is this dangerous, patients who don’t respond to the drug may be called “treatment failures” when the real drug would work.

The FDA is trying to crack down on this. Illegal batches are easy to spot. They list the parent company (Roche), not the subdivision that manufactures Avastin (Genentech). The label is in French, not English as for the real drug. The lot numbers are also different.

Avastin has received undue criticism for false promises, but it remains highly useful—and counterfeit versions remind us of how important the real version is. An important arrow in the oncologist’s quiver, Avastin should be championed, not undermined.

Marc Siegel, MD, is an internist and professor of medicine at New York University and the author of False Alarm: The Truth About the Epidemic of Fear