Activated STAT3 as a Correlate of Distant Metastasis in Prostate Cancer: A Secondary Analysis of Radiation Therapy Oncology Group 86-10

Objective

STAT3 participates in the regulation of cellular growth, survival, and oncogenesis. We evaluated the association between activated STAT3 expression and overall survival, disease-specific survival, distant metastasis, and local progression in a cohort of patients treated with either radiotherapy alone or radiotherapy plus short-term androgen blockade.

Methods

A total of 456 assessable patients were included in the Radiation Therapy Oncology Group 86-10 trial. Of these, 62 patients had sufficient tissue for the analysis of STAT3 expression by immunohistochemistry. Nuclear staining was quantified by an image analysis system.

Results

No significant difference was found in the distribution of clinical characteristics and assigned treatment between the patients available for STAT3 analysis (STAT3 cohort) and the others in the Radiation Therapy Oncology Group 86-10 trial (n = 394). Activated STAT3 correlated inversely with the development of distant metastasis (risk ratio [RR] = 0.81, P = 0.04) but not with overall survival, cause-specific survival, or local progression. Similar results were obtained when the data were dichotomized (ACIS index greater than 29%, RR = 0.41, P = 0.07). On multivariate analysis, activated STAT3 (continuous variable) was an independent predictor of distant metastasis (RR = 0.79, P = 0.04).

Conclusions

Activated STAT3 was inversely related to the development of distant metastasis in prostate cancer. This marker should be evaluated further in a larger cohort of patients.