Prolactin is a hormone produced in the pituitary gland. Previous studies have revealed that elevated levels of the hormone prolactin might be associated with an increased risk of breast cancer. Cabergoline has been shown to lower prolactin levels in the blood.

The purpose of this study is to evaluate the effectiveness of cabergoline in treating metastatic breast cancer disease in those who test positive for the prolactin receptor.

PRIMARY OBJECTIVES:

I. To evaluate overall response rate (ORR) of cabergoline in women with metastatic breast cancer.

SECONDARY OBJECTIVES:

I. Evaluate the progression-free survival (PFS) and overall survival (OS). II. Evaluate toxicity. III. Correlate serum prolactin levels during therapy with response. IV. Evaluate within-patient changes in computed tomography (CT) and bone scan measurements taken at baseline and after 2 cycles of treatment.

V. Evaluate within-patient changes in prolactin receptor (PRLr) expression from baseline to after 1 cycle of treatment in those patients who consent to optional repeat biopsy.

OUTLINE:

Patients receive cabergoline orally (PO) twice weekly for weeks 1-4. Courses repeat every 4 weeks in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed up at 30 days and then every 6 months thereafter.

Inclusion Criteria:

• Patients must have histologically confirmed metastatic breast cancer; tissue (a minimum of 3 slides) from the most recent biopsy is required for review and confirmation of eligibility; NOTE: material should ideally be from the metastatic disease, however material from the primary tumor is acceptable if that is all that is available

• Patients must have stage IV breast cancer

• Patients must have tumors (primary or metastatic) that stain positively for the prolactin receptor

• Patients may have measurable or evaluable disease

  • Measurable disease is defined as at least one lesion that can be accurately measured in at least one dimension (longest diameter to be recorded) as > 20 mm with conventional techniques or as > 10 mm with spiral CT scan
  • Evaluable disease is disease that does not meet the criteria for measurable disease; examples would include patients with effusions or bone-only disease

• Women of childbearing potential must commit to the use of effective barrier (non-hormonal) contraception while on study

• Patients must have a life expectancy of greater than 12 weeks

• Patients must have an Eastern Cooperative Oncology Group (ECOG) performance status =< 2

• Patients may have had a prior diagnosis of cancer if it has been > 5 years since their last treatment

• Leukocytes >= 3,000/uL (microliter)

• Absolute neutrophil count >= 1,500/uL

• Platelets >= 100,000/uL

• Child Pugh score =< 10

• Patients must be able to swallow and retain oral medication

• All patients must have given signed, informed consent prior to registration on study

Exclusion Criteria:

• Women who are pregnant or lactating are not eligible for study treatment

• Patients who are undergoing concomitant radiotherapy are NOT eligible for participation

• Patients who are receiving any other investigational agents or concurrent anticancer therapy are NOT eligible for participation; previous systemic treatment is allowed with a 2 week washout period prior to registration

• Patients who are taking any herbal (alternative) medicines are NOT eligible for participation; patients must be off any such medications by the time of registration

• Patients who are receiving concomitant D2-antagonists (such as phenothiazines, butyrophenones, thioxanthenes, or metoclopramide) are NOT eligible for participation; patients must be off any such medications by the time of registration

• Patients with known brain metastases are NOT eligible for participation

• Patients with any of the following conditions or complications are NOT eligible for participation:

  • Uncontrolled hypertension
  • Known hypersensitivity to ergot derivatives
  • History of cardiac valvular disorders, as suggested by anatomical evidence of valvulopathy of any valve (to be determined by pre-treatment evaluation including echocardiographic demonstration of valve leaflet thickening, valve restriction, or mixed valve restriction-stenosis)
  • History of pulmonary, pericardial, cardiac valvular, or retroperitoneal fibrotic disorders
  • Gastrointestinal (GI) tract disease resulting in an inability to take oral medication
  • Malabsorption syndrome
  • Require intravenous (IV) alimentation
  • History of prior surgical procedures affecting absorption
  • Uncontrolled inflammatory GI disease (e.g., Crohn's, ulcerative colitis)

Adverse events were collected over a 3 year period for the whole study. Patients were followed from treatment initiation, throughout treatment and 30 days post last treatment for up to 20 cycles (max number of cycles that any patient was treated) where 1 cycle equals 28 days.