Bone sialoprotein expression in primary human breast cancer is associated with bone metastases development

Breast cancer metastasizes to bone more frequently than to any other organ, and over 80% of advanced breast cancer patients develop bone metastases. Our recent demonstration that human breast cancer cells express bone sialoprotein (BSP), a bone matrix protein, provides a possible clue for the selective affinity of breast cancer cells for bone. We tested the hypothesis that detection of BSP in primary human breast cancer could be a potential indicator of the ability of breast cancer cells to metastasize to bone. BSP expression was evaluated in the primary breast cancers of 39 patients using immunoperoxidase and two specific anti-BSP antibodies. None of these patients presented clinically or scintigraphically detectable bone metastases at the time of surgery. In the course of their disease, 22 patients developed clinically diagnosed bone metastases. Expression of BSP in breast cancer cells from patients who developed bone metastases was significantly higher (p = 0.008, according to the Mann-Whitney test) than in patients with no bone involvement. No association was found between BSP expression in the primary breast lesions and axillary lymph node metastases. BSP expression was significantly increased in infiltrating ductal carcinoma compared with infiltrating lobular carcinoma (p = 0.0023). No correlation was found between immunoreactivity to BSP antibodies and estrogen receptor (ER) status, progesterone receptor (PR) status, or age. Our data suggest that BSP could help to identity which women will develop bone metastases and provide new bases for the understanding of the molecular mechanism(s) responsible for breast cancer cells osteotropism.