Breast cancer cells can acquire an osteoblast-like phenotype by ectopically expressing bone matrix proteins (e.g., bone sialoprotein (BSP) [4], osteopontin (OPN) [5], osteoprotegerin (OPG) [6] and secreted protein acidic and cysteine rich (SPARC)/osteonectin (ON) [7]), osteoblast-specific cadherins (e.g., cadherin 11 (CDH11) [8]), transcription factors that regulate bone remodeling (e.g., runt-related transcription factor 2 (RUNX2) [9]) and an “osteoblast gene signature” [2]. This evidence concerns the gene SPARC and breast cancer.