US regulators have approved AstraZeneca’s targeted monotherapy Iressa as a first-line treatment for certain patients with non-small cell lung cancer.

The US Food and Drug Administration has green-lighted the drug’s use to treat those with metastatic NSCLC whose tumours have epidermal growth factor receptor (EGFR) exon 19 deletions or exon 21 (L858R) substitution mutations.

The regulator has also cleared Qiagen's companion diagnostic test - therascreen EGFR RGQ PCR Kit - to determine which patients are suitbable for treatment.

Iressa (gefitinib) acts by inhibiting the tyrosine kinase enzyme in the EGFR, thus blocking transmission of signals involved in the growth and spread of tumours. EGFR mutations occur in around 10%-15% of NSCLC Caucasian patients and 30%-40% of NSCLC patients in Asia.

Approval was based in part on data from the Phase IV IFUM1 (IRESSA Follow-Up Measure) study, in which 70% of Caucasian patients taking part experienced some response (tumour shrinkage) to treatment with the drug.

On the safety side, the most common adverse events were found to be were rash (44.9%), diarrhoea (30.8%), vomiting (13.1%), asthenia, cough and dry skin (all 11.2%), and nausea (10.3%). Two patients (1.9%) experienced a serious AE related to treatment, and four (3.7%) discontinued because of side effects.

Iressa was first cleared in the US in 2003 as a third-line treatment for NSCLC under the FDA’s accelerated approvals process, but its use was later narrowed down to include only those with certain tumour characteristics after subsequent data indicated the overall survival benefit in the entire population was not superior to placebo.