Fulvestrant With or Without Bortezomib in Patients With Inoperable Locally Advanced or Metastatic Estrogen Receptor Positive Breast Cancer

PRIMARY OBJECTIVES: I. To determine if the addition of bortezomib to fulvestrant improves median progression free survival (PFS) compared with fulvestrant alone in postmenopausal women with estrogen receptor (ER)-positive locally advanced inoperable or metastatic breast cancer who have disease that is resistant to aromatase inhibitor therapy (Arms A versus \[vs.\] B). SECONDARY OBJECTIVES: I. To determine if the addition of bortezomib to fulvestrant improves the clinical benefit rate (defined as objective response plus stable disease for at least 24 weeks from day +1). II. To determine the percent of patients, treated with fulvestrant alone and fulvestrant plus bortezomib, who remain progression-free 24 weeks from day +1 (Arms A vs. B). III. To determine the overall survival of patients treated with fulvestrant alone and fulvestrant plus bortezomib (Arms A, B, C). IV. To determine the adverse event profile in patients treated with fulvestrant alone and fulvestrant plus bortezomib (Arms A, B, C). V. To determine the clinical benefit rate at 12 and 24 weeks of fulvestrant plus bortezomib in patients who have progressed on the fulvestrant alone arm and crossover to receive the combination (Arm C). TERTIARY OBJECTIVES: I. To perform an exploratory analysis of the effects of bortezomib (plus fulvestrant) in intratumoral nuclear/cytoplasmic ER ratio, unfolded protein response (BiP), apoptosis (cleaved caspase 3), B-cell chronic lymphocytic leukemia (CLL)/lymphoma 2 (Bcl-2) phospho c-Jun N-terminal kinase (JNK) in patients with tumors accessible to biopsy who consent to optional post-treatment biopsy. II. To determine with cyclin D1 expression in pretreatment tumor specimens (from metastatic disease or the primary tumor if the former is not available) is predictive of clinical benefit with fulvestrant-bortezomib. OUTLINE: Patients are randomized to 1 of 2 treatment arms (Arms A or B). ARM A: Patients receive fulvestrant intramuscularly (IM) on day 1 (days -14, 1, and 15 of course 1 only). Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. Patients with progressive disease may crossover to arm C. ARM B: Patients receive fulvestrant as in arm A and bortezomib intravenously (IV) on days 1, 8, and 15. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. ARM C: Patients receive fulvestrant IM on day 1 and bortezomib IV on days 1, 8, and 15. Courses repeat every 28 days in the absence of disease progression or unacceptable toxicity. After completion of study therapy, patients are followed up every 3 months.