Research into heat shock proteins (HSPs) for the clinical management of tumours has intensified as new evidence shows they can be used as biomarkers in carcinogenesis and are related to poor prognosis in some cancer types. Members of small HSP, HSP70 and HSP90 families have been studied extensively in breast cancer. This article reviews current understanding of the role of HSP and HSF-1 (Heat shock factor 1) expression in human breast cancer and looks at its potential diagnostic, prognostic and therapeutic value. The exciting progress that has been made using HSP 90 inhibitors in breast cancer treatment is examined and the results of preliminary studies on the expression of stress proteins in the animal model canine mammary tumours are also presented.