Hormone Receptor Positive Metastatic Breast Cancer (HR+ mBC) BIIB021 Plus Aromasin Schedule Finding

Inclusion Criteria:

Age 18 years of age
Must have histologically or cytologically confirmed estrogen receptor- positive or progesterone receptor-positive, incurable, locally advanced, or metastatic breast cancer.
Must have disease progression during treatment with a nonsteroidal AI for locally advanced or metastatic disease, or relapse during treatment or within 12 months of discontinuation of treatment in the adjuvant setting.
Must be a postmenopausal female.

Must have measurable or evaluable disease.

Measurable disease is defined as >=1 lesion with a diameter of >=10 mm
Evaluable disease is defined as bone lesions evaluable by plain X ray, CT scan, or MRI. Lesions identified only by radionuclide bone scan are not allowed.
One prior chemotherapy regimen for advanced mBC is allowed.
Prior radiotherapy is allowed.
Must be able to swallow and retain oral medication.
ECOG performance status of <=2

Required laboratory values

Plasma cortisol and adrenocorticotropic hormone (ACTH) levels that are not suggestive of adrenal insufficiency unless on replacement therapy for known adrenal insufficiency.

Exclusion Criteria:

HER2 overexpressing tumor.
History of central nervous system (CNS) metastasis.
Previous treatment with exemestane or treatment with an Hsp90 inhibitor.
Use of proton pump inhibitors.
Known history of or positive test result for hepatitis B or C or HIV.
History of gastrectomy or major surgery to small intestine.