Since presenting our positive clinical data at both ASCO and ECCO this year, we have had overwhelming interest in PLX4032 from physicians and patients worldwide. We are looking forward to advancing PLX4032 with the hope of registering this drug as soon as possible in order to make this medicine available to the many metastatic melanoma patients who may benefit, stated K. Peter Hirth, Ph.D., chief executive officer of Plexxikon. The data generated from the melanoma extension study clearly demonstrate single agent activity with PLX4032, which is unprecedented for melanoma. Additionally, the high degree of selectivity of PLX4032 has enabled us to dose to near complete target inhibition while such treatment has been well tolerated by most patients.

Melanoma Extension Study Confirms Safety & Tumor Regression Seen in Phase 1 Dose Escalation

In an extension study of melanoma patients with the BRAFV600E mutation, 31 patients have been enrolled, most with advanced metastatic disease (Stage M1c), and treated with PLX4032 at 960 mg BID. Among the 27 evaluable patients to date, results confirm the preliminary safety and efficacy seen in the previous Phase 1 dose escalation study:

PLX4032 was well tolerated at 960 mg BID, now confirmed as the maximum tolerated dose Complete response in 1 patient treated for 3 cycles Partial responses of greater than 30% tumor regression by RECIST criteria have been observed in 18 patients, with 15 patients showing responses of greater than 50% Minor responses in 6 patients showed tumor regression between 10% and 30%

A median PFS has not been achieved since it is too early in the study to report. These data were presented earlier this month at the ECCO 15 / ESMO 34 2009 Conference in Berlin, Germany.

Drug-related adverse events were predominantly mild in severity and included rash, joint pain, photosensitivity and fatigue. Serious adverse events were observed in some patients after chronic treatment, including seven patients with cutaneous squamous cell carcinoma (keratoacanthoma subtype) that were treated by excision, while treatment with PLX4032 was continued. A risk management plan is in place for baseline evaluation of the skin and monitoring of all patients while on study.

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