Yamashita H et al. (2006) Stat5 expression predicts response to endocrine therapy and improves survival in estrogen receptor-positive breast cancer. Endocr Relat Cancer 13: 885–893

Members of the signal transducers and activators of transcription (Stat) family have been associated with oncogenesis; constitutively active forms of Stat3 and Stat5 can promote cell proliferation and prevent apoptosis in various cancers. In human breast cancers, nuclear localization and phosphorylation of Stat5 is strongly associated with improved disease-free and overall survival. Yamashita et al. have now demonstrated that Stat5 expression is a prognostic marker of overall survival in patients with estrogen receptor (ER)-positive breast cancer.

The study included 517 breast tumor specimens from patients who had undergone surgical treatment for primary invasive carcinomas. Immunohistochemical analysis showed that Stat3 expression was closely associated with expression of Stat5 (P <0.0001), but there was no association between Stat3 expression and clinicopathological factors. By contrast, Stat5 expression strongly correlated with histological grade (P <0.0001), and was also associated with ER (P = 0.02) and progesterone receptor (P = 0.026) expression. Although Stat5 expression was not correlated with disease-free survival, it was associated with an increased overall survival in patients with ER-positive breast cancer (P = 0.0009). No association between Stat3 and survival was noted. Moreover, the authors showed that patients with Stat5-positive primary tumors responded better to endocrine therapy (P = 0.04), and that Stat5 expression was significantly associated with longer survival after relapse (P = 0.0003).

The authors conclude that Stat5 is an independent prognostic molecular marker of overall survival in ER-positive breast cancer patients and a predictive factor for endocrine therapy response, indicating that this marker could be used to select patients who might benefit from endocrine therapy.