STAT3 is an oncogene that regulates critical cellular processes and whose constitutive activation has been demonstrated to correlate with biological and clinical features in many types of human malignancy. In this study, STAT3 activation was assessed in the Ewing sarcoma family of tumours (ESFT), which is characterized by fusion of the EWS gene with one of several Ets transcription factors, most commonly EWS-FLI1. STAT3 activation was assessed by immunohistochemistry using a monoclonal antibody specific for tyrosine(705)-phosphorylated STAT3 (pSTAT3(tyr705)) and a tissue microarray containing 49 paraffin-embedded ESFT tumours with known EWS translocations. Twenty-five (51%) tumours were pSTAT3(tyr705)-positive, as defined by more than 10% tumour cell immunostaining. STAT3 activation correlated with tumour site at presentation, with pSTAT3(tyr705)-negative ESFT involving axial sites predominantly (p = 0.008). Notably, among 31 patients who presented with localized disease, high-level STAT3 activation correlated with better overall survival (p = 0.02). STAT3 activation was not directly related to EWS-FLI1 expression, since EWS-FLI1 transfection did not result in STAT3 activation. Furthermore, detailed molecular analysis indicated that STAT3 activation may be seen with EWS-FLI1 or EWS-ERG and appears to be independent of EWS-FLI1 fusion type. In conclusion, STAT3 activation is present in approximately half of ESFT and correlates with clinical features. The role of STAT3 activation in ESFT pathogenesis seems to be independent of the type of EWS/Ets translocation.

Signal transducers and activators of transcription (STAT)-3 is an oncogenic protein that is constitutively activated in many human cancers, including 30 to 60% of primary breast cancer. The biological significance of STAT3 activation in breast cancer is not fully understood. We have previously shown that STAT3 up-regulates tissue inhibitors of metalloproteinase (TIMP)-1, a cytokine known to block metalloproteinases and decrease invasiveness in certain cancer cell types. We hypothesize that STAT3 activation may modulate tumor invasiveness of breast cancer by regulating TIMP1 expression. Using MCF-7 cells transfected with tetracycline-off STAT3C (constitutively active STAT3), we generated an in vitro system in which STAT3C levels can be tightly controlled in breast cancer cells. Increasing tetracycline levels gradually decreased STAT3C and TIMP1 in a dose-dependent manner, and down-regulation of these proteins led to a reciprocal decrease in invasiveness of these cells in Matrigel. Addition of a neutralizing anti-TIMP1 antibody increased invasiveness in the same experimental system. Using immunohistochemistry and 142 primary breast tumors, we found a significant association between the expression of the phosphorylated/active form of STAT3 (pSTAT3) and that of TIMP1. Importantly, STAT3 activation correlated significantly with a lower frequency of vascular and lymphatic invasion (P ‫؍‬ 0.015 and P ‫؍‬ 0.0002, respectively). Our data support the concept that STAT3 activation significantly modulates the biological and clinical behavior of breast cancer.