AstraZeneca K.K., the Osaka-based importer of the controversial cancer drug Iressa, may have failed to notify health authorities of the drug's acute side effects within the time period set by the government, sources said Friday.

The Health, Labor and Welfare Ministry has launched an investigation to determine whether AstraZeneca violated the Pharmaceutical Affairs Law. If found in breach of the law, the firm may face disciplinary action, including an order to halt operations.

Iressa, known by its generic name gefitinib, has been administered to about 23,000 patients so far, 183 of whom have died after suffering from side effects.