Drug firm AstraZeneca India on Friday said it has received approval from the domestic drug regulator to market a drug to treat biliary tract cancer (BTC) in the country. The company has received approval from the Central Drugs Standard Control Organisation (CDSCO) for Durvalumab, the drug firm said in a statement. BTC is a group of rare and aggressive gastrointestinal (GI) cancers that form in the cells of the bile ducts (cholangiocarcinoma), gallbladder or ampulla of Vater (where the bile duct and pancreatic duct connect to the small intestine).