Bache et al. BMC Cancer 2010, 10:132 http://www.biomedcentral.com/1471-2407/10/132 Page 4 of 8 Figure 1 OPN levels in serum and tumor tissue of STS patients. different clinical parameters. In particular, high serum OPN protein levels correlated with high tumor stage (p = 0.004), grade of tumors (p = 0.003) and tumor size (p = 0.03). Additionally, all patients with early distant metastasis (7/86) had a high median serum OPN protein level of 1301 ng/ml (1009 to 2660 ng/ml) compared to patients without distant metastasis (79/86) who had a median serum OPN protein level of 657 ng/ml (183 to 1873 ng/ml). However, the difference was not significant (Table 3). A high tumor OPN protein level was signifi- cantly related to tumor grade (p = 0.003) and an increased rate of relapse (p = 0.02), and also showed a trend association with high tumor stage (p = 0.06) (Table 3). Furthermore, plasma OPN protein levels sig- nificantly correlated with tumor type (p = 0.002) whereas tumor OPN protein levels displayed only a trend association with tumor type (p = 0.07). Moreover, the patient group with the lowest serum and tumor OPN protein level was composed of 57% and 48% lipo- sarcoma patients, respectively. In contrast, the three remaining patient groups with a high serum (>516.54 ng/ml) and tumor (>34.34 ng/mg) OPN protein level were composed of more than 80% of patients with malignant fibrous histiocytoma (MFH), fibrosarcoma (FS), leiomyosarcoma (LMS), rhabdomyosarcoma (RMS). In contrast to protein expression, statistical ana- lysis of OPN mRNA levels showed no association with clinical parameters or clinical outcome (Table 3). Discussion OPN overexpression is linked to an unfavorable prog- nosis in a variety of human cancers. However, only a few studies to date have investigated the prognostic impact of osteopontin in sarcoma patients. In the pre- sent study, we analyzed OPN mRNA and protein levels in tumors and the OPN protein levels from the serum of 93 soft tissue sarcoma patients and correlated OPN levels with clinical parameters and prognosis. In our study no correlation was found between OPN levels in serum and tumor tissue. It is well known that extracellular OPN is involved to tumor progression with signaling to proliferation, migration and survival. Also intracellular OPN is involved in cell migration [29]. Additionally, there is also evidence that suggests that intracellular OPN has other cellular functions, particu- larly in relation to cell proliferation [30]. But regulation between intra- and extracellular OPN forms remains unknown. Nordsmark et al. (2007) assume a relation between plasma concentration of OPN and intratumoral OPN production [31]. However, in agreement with our