A Study of Abiraterone Acetate Plus Prednisone With or Without Exemestane in Postmenopausal Women With Estrogen Receptor-Positive (ER+) Metastatic Breast Cancer Progressing After Letrozole or Anastrozole Therapy

Inclusion Criteria:

* Female patients must be postmenopausal
* ER+, Human epidermal growth factor receptor 2 (Her2) negative metastatic breast cancer
* Disease must have been sensitive to anastrozole or letrozole therapy prior to disease progression
* No more than two prior lines of therapy in the metastatic setting, of which no more than one was chemotherapy
* Eastern Cooperative Oncology Group (ECOG) performance status score of \<=1
* Patients with disease confined only to bone may be included, but patients with purely sclerotic lesions may not participate in the study

Exclusion Criteria:

* Prior treatment with exemestane, ketoconazole, aminoglutethimide, or a CYP17 inhibitor. Prior treatment with ketoconazole for \<= 7 days is permitted and topical formulations of ketoconazole are permitted
* Potential patients must not have taken anastrozole, letrozole, fulvestrant, or any chemotherapy for at least 2 weeks (bevacizumab for at least 3 weeks) before randomization
* Anticancer immunotherapy or investigational agent within 4 weeks before randomization, or anticancer radiotherapy (except palliative) or anticancer endocrine therapy within 2 weeks before randomization
* Serious or uncontrolled nonmalignant disease, including active or uncontrolled infection
* Clinical or biochemical evidence of hyperaldosteronism or hypopituitarism
* Any condition that, in the opinion of the investigator, would compromise the well-being of the patient or that could prevent, limit, or confound the protocol-specified assessments