Loss of nuclear Stat5a (Nuc-Stat5a) predicts unfavorable breast cancer prognosis. (A, B) Nuclear localization of Stat5a was detected with standard DAB IHC and pathologist review of whole-tissue sections in Material III. Kaplan-Meier analysis indicated that patients with low levels of Nuc-Stat5a had (A) reduced time-to-recurrence (TTR) of breast cancer and (B) poor breast cancer-specific survival (CSS). (C, D) Nuclear localization of immunofluorescently labeled Stat5a was quantified by AQUA analysis in a tissue microarray of node-negative breast cancer. (C) Representative immunofluorescent images of high and low Stat5a expression in invasive ductal carcinoma. (D) Quantitation of nuclear levels of Stat5a by AQUA revealed by Kaplan-Meier analysis that loss of Nuc-Stat5a is prognostic of poor breast cancer-specific survival (CSS) in Material IV. Censored cases (+) and number of patients per group are indicated.