Based on the anti-tumor potential seen pre-clinically with Hsp90 inhibition, the potent effects of STA-9090 seen pre-clinically as compared with other inhibitors in the same class, as well as early data suggesting safety and tolerability of this drug in the Phase I setting, we propose to study the single-agent activity of STA-9090 in a Phase II trial of patients with relapsed or refractory small cell lung cancer.