Small integrin-binding ligand N-linked glycoproteins (SIBLINGs) constitute a family of extracellular matrix proteins involved in bone homeostasis. Their pattern of expression has been primarily reported in bone and tooth and, more recently, in several cancer types. Dentin matrix protein 1 (DMP1), a SIBLING family member, expression was investigated by immunohistochemistry in a retrospective series of 148 primary human breast cancers. Correlations between DMP1 expression levels in the tumors and clinicopathologic features, bone metastases development and relapse of the disease were examined. DMP1 was expressed by 63.5% of the breast tumors analyzed. Significant inverse associations were found between DMP1 expression levels and the size and grade of the tumors (both, P