The present study demonstrates that a high level of YY1 protein expression increases the risk of metastasis (4.69-fold) and poor survival (8.35-fold) in osteosarcoma patients independently of covariates such as age, gender, histotype, and chemonecrosis. We report that the highest range of YY1 expression is a statistically significant prognostic factor setting the 5-year survival rate to 34% in patients with osteosarcoma. These results are in line with literature data and with the tumor necrosis rate which is currently the strongest clinical prognostic factor after chemotherapy [2, 23, 24].
Overall, the molecular complexity of osteosarcoma makes the known prognostic markers of limited utility [12, 25]. A multiple panel of biomarkers in addition to clinical parameters would be useful for predicting prognosis . In this setting, YY1 is the first osteosarcoma marker whose overexpression has been correlated with low metastasis-free and poor overall survival in a higher frequency of cases (61% in the present study) than reported in other studies leading us to set a higher cut-off value (YY1 > 50%) . In addition, low YY1 expression was correlated with best clinical prognosis and absence of metastasis during follow-up. One common limitation of immunohistochemical studies is both antibody sensitivity and specificity. To address these issues, we used an antibody previously tested by other groups [26, 27]. Immunohistochemistry was also performed in two different Institutions which studied different subgroups of patients [26, 27]. YY1 was localized in the nucleus irrespective of histologic subtype, patient age, or tumor site. Although this is a small study, there was no significant difference in YY1 scores between younger and older age groups suggesting its role in tumor development. The design of the present study stemmed from our previous in vitro observations demonstrating that YY1 was overexpressed in osteosarcoma cells and tissues with more aggressive phenotype [16–18]. This is in agreement with YY1 overexpression in prostate, gastrointestinal [26, 27] and other tumors . Moreover, in an in vivo mice model of osteosarcoma YY1 was also shown to play a key role in metastatic growth  by regulating vascular supply [20, 28].
Interestingly, the majority of patients analyzed revealed strong YY1 expression and showed poor response to chemotherapy based on Huvos grading system. Although the correlation between YY1 expression and prognosis may merely be a statistical association, the protein dosage points to a functional relationship between YY1 overexpression and a more aggressive tumor phenotype. Noteworthy, literature data from other tumoral and non-tumoral tissues provide at least some evidence for the proposed functional relationship. Resistance to Fas-mediated apoptosis of prostate cancer cells is linked to YY1 . A further potential link between YY1 overexpression and chemoresistance lies in the fact that YY1 regulates DR5 gene . We have recently demonstrated that YY1 is involved in CXCR4 and VEGF pathways [19, 20] which have both been genetically amplified and correlated with poor survival of soft-tissue sarcomas [8, 31, 32]. In addition, YY1 overexpression increases resistance to taxana treatment in epithelial ovarian cancer . Furthermore, in a meta-analysis, YY1 was scored as the most significant gene upregulated in metastatic breast cancer . Thus, YY1 screening may be useful in optimizing individual therapy management at the time of diagnosis in these patients.
In conclusion, we demonstrated for the first time that high YY1 expression in osteosarcoma is associated with metastasis development and mortality independently of age, gender, histotype and presence of metastasis at baseline. While other studies have analyzed larger cohorts of patients [34, 35], this is the first time a prognostic marker has demonstrated poor outcome by multivariate analysis. If data are confirmed in a larger cohort of patients, YY1 may become part of a multiple panel of biomarkers clinically useful for osteosarcoma prognosis.