The purpose of this study is to determine the safety, tolerability and maximum tolerated dose of IPI-504 in patients with non-small cell lung cancer (NSCLC). The study will examine how IPI-504 is absorbed, distributed, metabolized and eliminated by the body. The study will also evaluate the anti-tumor activity of IPI-504.

IPI-504 is a novel small molecule inhibitor of heat shock protein 90 (Hsp90), an emerging and recently identified target for cancer therapy. Hsp90 is a protein chaperone that plays a central role in maintaining the proper folding, function and viability of various "client proteins". Many of the client proteins stabilized by Hsp90 are oncoproteins and cell-signaling proteins important in cancer cell proliferation and cancer cell survival. This clinical trial will study the effects of IPI-504 in a molecularly defined sub-group of patients who carry client proteins found in non-small cell lung cancer.

Inclusion Criteria:

• Pathologically confirmed diagnosis of a Stage IIIb (with malignant pleural or pericardial effusion) or Stage IV NSCLC
• Measurable disease by RECIST criteria.

Exclusion Criteria:

• Treatment for NSCLC with any approved or investigational product within 2 weeks of the start of IPI-504 treatment for any small molecule therapy; within 4 weeks of the start of IPI-504 treatment for any biologic or any conventional chemotherapy.
• Inadequate hematologic or renal or hepatic function
• Previous treatment with 17-AAG, DMAG or other known Hsp90 inhibitor.