Signal transducer and activator of transcription-3 and breast cancer prognosis

Abstract

Signal transducer and activator of transcription-3 (Stat3) is frequently activated in breast cancer and multiple lines of evidence suggest that Stat3 promotes tumor progression. However, the prognostic value of Stat3 in human breast cancer remains controversial and associations range from favorable to unfavorable based on four outcome studies of 62, 102, 255 and 517 patients. Cellular Stat3 protein expression was measured in three studies whereas nuclear localized, tyrosine phosphorylated Stat3 (Nuc-pYStat3) was used as the readout in only one study. We therefore retrospectively analyzed the prognostic value of Nuc-pYStat3 in a larger material of 721 breast cancer specimens. Overall, patients whose tumors were positive for Nuc-pYStat3 tended to have improved survival, but the trend did not reach statistical significance (P=0.08). When specimens were stratified by tumor grade, patients with low grade but not high grade tumors that were positive for Nuc-pYStat3 had significantly prolonged overall survival in univariate analysis (P=0.014) but not in multivariate analyses. Unexpectedly, quantitative immunofluoresence detection revealed highest levels of Nuc-pYStat3 in normal breast epithelia and gradual loss of Nuc-pYStat3 during progression from DCIS, invasive ductal carcinoma, and lymph node metastases. Levels of Nuc-pYStat3 correlated positively with levels of Nuc-pYStat5, a favorable prognostic marker, in invasive ductal carcinomas. Furthermore, NucpYStat3 levels correlated strongly with protein levels of nuclear localized Stat5a (r=0.633, P<0.001) but not Stat5b. Our data does not support the notion that Nuc-pYStat3 is an independent marker of prognosis in breast cancer, although future studies may reveal prognostic utility within molecularly characterized subtypes of breast cancer.

Keywords: Stat3; biomarker; breast cancer; immunohistochemistry; prognosis; survival.

Figure 1

Distribution of nuclear phospho-Stat3 (Tyr705) immunohistochemical staining scores in breast cancer. A. Example of breast carcinoma with negative phospho-Stat3 staining (upper panel) and positive phospho-Stat3 staining using diaminoben-zamide chromogen (score 3; lower panel); B. Distribution of phospho-Stat3 (Tyr705) nuclear staining scores 0-3.

Figure 2

Kaplan-Meier survival curves in breast cancer according to nuclear phospho-Stat3 (Tyr705) staining status. A. Survival curves for all samples; B. Survival curves for low grade cancer (grades 1 and 2); C. Survival curves for high grade cancer (grade 3).

Figure 3

AQUA analysis reveals Stat5 and Stat3 are correlated in human breast cancer. A. Immunofluorescent staining of human breast cancer tissues using pY-Stat3(red) or pY-Stat5(red), Cytokeratin(green), and Dapi(blue). Representative correlative images of normal tissue showing high expression of nuclear pY-Stat5 and pY-Stat3, Case 1 showing moderate expression of nuclear pY-Stat5 and pY-Stat3, and Case 2 showing no expression of nuclear pY-Stat5 and pY-Stat3. B. AQUA quantification of nuclear pY-Stat3 and pY-Stat5 protein levels in normal, DCIS, invasive ductal carcinomas, and lymph node metastases (left panel). Correlation analyses of nuclear pY-Stat5 and pY-Stat3 proteins in human breast cancer samples (right panel). C. Correlation analyses of nuclear Stat5a or b and pY-Stat3 proteins in human breast cancer samples.