The news this week that a fake version of the cancer medicine Avastin has made its way into the United States highlights a longtime concern: There are few safeguards to make sure fake drugs can be spotted before they make it to your doctor’s office. For more than a decade, public safety advocates have called for a tracking system that would enable everyone from manufacturers to wholesalers to doctors to verify the authenticity of prescription drugs through electronic tags or barcodes. But bickering between those parties over the cost and scope has stalled the effort.