Inclusion Criteria:

- Written informed consent.

- Age >= 18 years old.

- Metastatic breast cancer patients with lytic, sclerotic or mixed bone lesions.

- Non-symptomatic bone lesions, defined as pain absence, lack of bone complications
(fracture, hypercalcemia, central nervous system [CNS] compression), no need of
analgesic chronic administration for bone disease.

- A maximum of two chemotherapy lines for metastatic disease.

- A maximum of two hormone therapy lines for metastatic disease.

- Normal, minimally altered renal function (serum creatinine < 1.5 x upper normal limit
[UNL]).

- Normal serum calcium levels.

- Performance status 0,1 (World Health Organization [WHO]).

- Negative pregnancy test before study recruitment.

Exclusion Criteria:

- Previous treatment with bisphosphonates or raloxifene in the 30 days prior to
randomization.

- Metastasis in CNS.

- History of hypersensitivity to bisphosphonates.

- Pregnant or lactating women.

- Third chemotherapy line for metastatic disease.

- Third hormone therapy line for metastatic disease.

- Males.