Résumé
Introduction: Currently, very few studies are available concerning the mammalian Hippo pathway in bone sarcomas. YAP/TAZ transcription co-activators are key downstream effectors of this pathway and may also have oncogenic properties. Additionally, recent in-vitro experiments showed that expression of beta 1-integrin promoted metastasis in osteosarcomas. This study investigated the expression of YAP/TAZ and beta 1-integrin in human osteosarcomas.
Materials and methods: We performed automated immunohistochemistry on tissue-microarrays (TMA) in which 69 conventional osteosarcomas biopsies performed prior to chemotherapy were embedded. Cellular localization and semi-quantitative analysis of each immunostain was performed using Immunoreactive Score (IRS) and correlated to clinico-pathological data.
Results: Cytoplasmic expression of beta 1-integrin was noted in 54/59 osteosarcomas (92%), with 33/59 cases (56%) displaying membranous staining. YAP/TAZ was expressed in 27/45 osteosarcomas (60%), with 14 cases (31%) showing cytoplasmic expression while 13 other cases (28%) displayed nuclear expression. No link was found between YAP/TAZ or beta 1-integrin expression and response to chemotherapy. In univariate analysis, YAP/TAZ immunoreactive score was pejoratively correlated with overall survival (p = 0.01). Expression of beta 1-integrin on cell membrane was also pejorative for OS (p = 0.045). In multivariate analysis, YAP/TAZ nuclear expression was an independent prognostic factor for PFS (p = 0.035).
Conclusion: this study indicates that beta 1-integrin and YAP/TAZ proteins are linked to prognosis and therefore could be therapeutic targets in conventional osteosarcomas.