Recently, using an ultrasensitive time-resolved immuno-fluorometric assay, PSA immunoreactivity (IR-PSA) was found in breast tumor cytosols. We retrospectively studied 219 breast cancer patients, measuring IR-PSA in the tumor cytosols, and classified the breast cancers as either PSA positive or PSA negative based on an IR-PSA cut off level of 1 pg/mg. Multivariated analysis showed that IR-PSA is an independent favourable prognostic indicator for postmenopausal, node positive breast cancer patients. Additionally, IR-PSA correlates with reduced risk of relapse in ER+ve tumors and is negatively correlated with mutated p53, which increases the risk of relapse.