EXPRESSION OF BONE SIALOPROTEIN, A BONE-MATRIX PROTEIN, IN HUMAN BREAST-CANCER

Microcalcifications are often associated with human mammary lesions, p articularly with breast carcinomas. To date, the molecular mechanism t hat leads to the deposition of hydroxyapatite in the mammary tissue ha s not been elucidated. Bone sialoprotein (BSP) is a glycoprotein the e xpression of which coincides with the appearance of the first hydroxya patite crystals during bone development. In this study, we report the observation that BSP, a bone matrix protein, is expressed in human mam mary cancer cells. Using an immunoperoxidase technique, we studied the expression of BSP in 79 breast lesions, including 28 benign and 51 ma lignant specimens. Two polyclonal antibodies, one directed against int act human BSP and the other against a synthetic peptide of BSP (residu es 277-294), were used and gave identical results. Normal mammary glan ds expressed undetectable or barely detectable amounts of BSP, and the majority of the benign lesions examined were generally unstained (0) or weakly stained (1+). Most of the breast carcinoma specimens (around 87%) showed a significant increase (P = 0.0001) in BSP expression. Br east carcinomas with microcalcifications had the highest immunoreactiv ity (2+ or 3+) to BSP antibodies. This is the first demonstration that BSP expression is significantly increased in breast cancer. Expressio n of BSP by breast cancer cells could play a major role in the deposit ion of microcalcifications and in the preferred bone homing of breast cancer cells.