Clinical significance of osteoblast precursors and osteoclast precursors in earlier diagnosis and monitoring of myeloma bone disease.

Bone disease is the most common complication of multiple myeloma (MM). In order to diagnose and monitor the bone damages earlier, we detected circulating osteoclast precursors (OCPs) and osteoblast precursors (OBPs) by flow cytometry, comparing with special biochemical markers, such as tartrate-resistant acid phosphatase isoform 5b (TRACP-5b), carboxy-terminal cross-linking telopeptide of type I collagen (CTX), osteocalcin (OCN), and procollagen I amino-terminal propeptide (PINP). The results showed that the circulating OBPs in the newly diagnosed MM patients significantly decreased compared with the normal controls (7.14 vs 12.82 %, P = 0.045), while circulating OCPs in the newly diagnosed patients and remission patients were significantly increased than the normal controls (2.46 vs 0.17 %, P = 0.000; 1.87 vs 0.17 %, P = 0.000, respectively). According to X-ray, newly diagnosed patients were divided into stages A and B (without and with osteolytic lesions). Compared with the normal controls, the circulating OBPs in stages A and B reduced (12.82 vs 7.47 %, P = 0.041; 12.82 vs 7.14 %, P = 0.010, respectively), while the circulating OCPs elevated (0.17 vs 2.31 %, P=0.010; 0.17 % vs 2.71 %, P=0.001, respectively). The levels of TRACP-5b and CTX in the newly diagnosed patients were higher than the normal controls (P = 0.014, P = 0.037) and remission patients (P = 0.025, P = 0.003), and they were significantly higher in stage B than the normal controls (P = 0.015, P = 0.002). However, the PINP and OCN levels had no significant changes in different stages. In conclusion, abnormal circulating OBPs and OCPs were found earlier before X-ray in MM and still existed in remission patients, indicating that they may be novel predictive markers for early diagnosing and monitoring bone disease.