 In one phase II multicenter study, 63 women with metastatic breast cancer who could have had any number of previous chemotherapy or hormonal regimens were treated with an oral daily dose of 500 mg of ZD1839 until disease progression, intolerable toxicity, or withdrawal of consent. Dosage reduction to 250 mg daily was allowed for toxicity. The primary end point was clinical benefit rate complete response partial response modified ICCWHO criteria stable disease at 6 months. There was 1 partial response and 2 patients with stable disease for more than 4 months 4 months in 1 patient and 7 months in the other, for a total of 4.8 clinical benefit. An additional 4 patients had stable disease lasting 1 to 2 months, and another 2 patients had stable disease lasting 1 month, resulting in an overall 14.3 partial response or stable disease in this heavily pre-treated population; 15 were on treatment for 4 to 8 months, and 2 patients stayed on treatment, despite progression, because of significant bone pain palliation. 