Inclusion Criteria:

- Subjects with histologically or cytologically confirmed solid tumors who have failed
or are not candidates for standard therapies or for whom no approved therapy is
available.

- Eastern Cooperative Oncology Group (ECOG) performance status of greater or equal to
2.

- Medically able to tolerate a high fat meal and to fast as per protocol.

- Expected survival time of at least 3 months in the opinion of the Investigator.

- Ability to take ranitidine as per protocol.

- Must be able to swallow and retain oral medication.

- Lab values consistent with adequate renal, hepatic, and bone marrow functions.

- Electrocardiogram (ECG) with QTc of ≤450 msec for men or ≤470 msec for women and no
clinically significant findings.

Exclusion Criteria:

- Pregnant (positive pregnancy test) or nursing women.

- Previous treatment with an Hsp90 inhibitor.

- Use of antacids within 7 days of Study Day 1.

- Prior antitumor therapies, including prior experimental agents or approved antitumor
therapies within 28 days of the first dose of BIIB021.

- Major surgery or radiation within 28 days of the first dose of BIIB021.

- Uncontrolled, severe medical illness, which in the opinion of the Investigator and/or
Sponsor could compromise protocol objectives.

- History of gastrectomy or major surgery to small intestine.

- History of exocrine pancreatic insufficiency.

- Chronic diarrhea (excess of 2 to 3 stools/day above normal frequency).

- Active bacterial or viral infection requiring concurrent treatment.

- History of hepatitis B or C or human immunodeficiency virus.

- History of central nervous system metastasis.

- Any thrombotic event occurred <3 months prior to Day 1.

- Conditions that may predispose subjects to seizures: History of seizure, previous
significant head trauma

- Drug or alcohol abuse.