Inclusion Criteria:

- Female

- 18 years of age or older

- Postmenopausal

- Histologically or cytologically confirmed adenocarcinoma of the breast with locally
advanced or metastatic disease this is not considered amenable to curative treatment
with elevation of CA 15-3 documented at the time of diagnosis of metastatic disease
and prior to initiation of letrozole or anastrozole therapy

- Current letrozole or anastrozole monotherapy with a documented CA 15-3 level that has
decreased by at least 50% of the patients baseline

- Letrozole or anastrozole must be discontinued at the time of study enrollment

- Evidence of hormone sensitivity of primary or secondary tissue.

- Measurable or nonmeasurable (but evaluable-defined as nontarget lesions) disease
according to modified RECIST

- Prior antiestrogen therapies including tamoxifen, steroidal AIs, nonsteroidal AIs, or
fulvestrant in the adjuvant setting is allowed provided the patient is currently on
letrozole or anastrozole monotherapy as first-line therapy for metastatic disease

- Life expectancy of greater than 3 months

- ECOG Performance Status of 0,1, or 2

- Normal organ and marrow function as outlined in protocol

Exclusion Criteria:

- Premenopausal

- Trastuzumab or biologic therapy within 2 weeks

- Prior or planned radiation therapy to a site of evaluable disease in the event that
the site is the only site of evaluable disease

- Concomitant anticancer treatments including trastuzumab, chemotherapy, or other
biologic agents other than letrozole or anastrozole therapy

- Chronic bisphosphonates for hypercalcemia or prevention of bone metastases.

- Treatment with non-approved or investigational agent within 2 weeks before study
entry

- Presence of life-threatening metastatic disease, defined as extensive hepatic
involvement, or past or present brain or leptomeningeal involvement, or symptomatic
pulmonary lymphangitic spread

- Patients who are highly symptomatic from their breast cancer, or who require urgent
palliative chemotherapy, as decided by their treating physician

- Previous or current systemic malignancy within the past five years, except for
contralateral breast carcinoma, in situ carcinoma of the cervix treated by cone
biopsy, or adequately treated basal or squamous cell carcinoma of the skin.

- Any severe concomitant condition believed to render subject undesirable for
participation