The US Food and Drug Administration this week approved AstraZeneca's new cancer drug gefitinib (Iressa), the first of a new class of cancer drugs billed as a well tolerated alternative to conventional chemotherapy. But the approval for use in non-small cell lung cancer was conditional on further studies, and the drug will not be prescribed for first line treatment as originally intended.

Gefitinib belongs to a class of drugs known as epidermal growth factor receptors, which block signals in cancer cells that promote growth. It was approved in Japan in July 2002, but the manufacturer's …