STAT3 and breast carcinoma: Interestingly, although it has been shown that Stat3 expression and activation is commonly found in breast cancer cells [15], and this transcription factor activation resulted in the malignant transformation of fibroblasts [43] and the proliferation of mammary tumor cells [4,6,44,45], there is also evidence that Stat3 activation in human breast cancer is associated with a better prognosis [46].