Zeneca (officially Zeneca Group PLC) was a British multinational pharmaceutical company headquartered in London, United Kingdom. It was formed in June 1993 by the demerger of the pharmaceuticals and agrochemicals businesses of Imperial Chemical Industries into a separate company listed on the London Stock Exchange. In 1999, Zeneca and the Sweden-based pharmaceutical company Astra AB merged to form AstraZeneca plc. Zeneca's largest therapeutic area was oncology, in which its key products included Casodex, Nolvadex and Zoladex. Other key products included heart drug Tenormin.