Furthermore, various serum markers, including tartrate-resistant acid phosphatase (TRACP) [104], procollagen type I N-terminal propeptide (P1NP) [105], and secreted Y-box binding protein 1 (sYB-1) [106], are associated with bone metastasis in breast cancer, with some markers showing potential for dynamic monitoring and improved diagnostic accuracy, though combined analysis with CTCs remains underexplored. This evidence concerns the gene ACP5 and breast cancer.