The purpose of the study is to see if daily and twice daily administration of BIIB021 is tolerated in patients with advanced solid tumors.

Heat shock protein 90 (HSP90) inhibitors are anticipated to have clinical activity in solid tumors because Hsp90 is required for the folding, activation, and assembly of many proteins involved in cancer cell survival, proliferation, and metastasis. The maximum tolerated dose (MTX) for BIIB021 administered twice weekly in a phase I study in subjects with advanced solid tumors have been defined at 600mg. It is now reasonable from a safety perspective and desirable from a pharmacokinetic perspective to evaluate more frequent dosing intervals in solid tumors with the goal of providing more sustained and completed inhibition of Hsp90.

Inclusion Criteria:

Subjects with histologically or cytologically confirmed solid tumor who have failed or refused standard therapies or for which no approved therapy is available.

Age greater than or equal to 18 years at the time of informed consent. ECOG performance status of less than or equal to 2. Lab values consistent with adequate renal, hepatic, and bone marrow functions.

Exclusion Criteria:

Prior antitumor therapies, including prior experimental agents or approved antitumor small molecules and biologics within 28 days and all associated toxicities resolved to eligibility levels.

Subjects with known brain metastases. Concurrent severe or uncontrolled medical disease. Must utilize effective contraception.