This study is a multicentre, open label, non-comparative, two stage phase II trial to assess the activity of ZD1839 (IRESSA) in patients with malignant mesothelioma. Patients will receive trial treatment as first-line therapy, administered continuously once daily until the completion of six 4-week cycles of treatment, disease progression, unacceptable toxicity or withdrawal of consent. Patients continuing to show evidence of response, disease stabilization or clinical benefit from ZD1839 may continue to receive therapy beyond completion of the trail.

Inclusion Criteria:

• Histologically-confirmed malignant mesothelioma (based on pleural biopsy); eligibility for first line therapy for malignant mesothelioma
• Uni or bi- dimensionally measurable disease
• No prior radiotherapy within 3 weeks of enrolment into the trial
• No significant comorbid disease

Exclusion Criteria:

• Other malignancies, either co-existing or diagnosed within the last 5 years, with the exception of basal cell carcinoma or cervical cancer in situ
• Brian metastasis or leptomeningeal carcinomatosis
• Any unresolved chronic toxicity greater than CTC grade 2 from previous anticancer therapy
• Concomitant use of phenytoin, carbamazepine, barbiturates, rifampicin, or St. John's Wort