The aim of our study was to evaluate the relationship between the expression of HSP70 protein, cell proliferation, the expression of ER receptors and the clinicopathological variables Grade and LNS in breast invasive human tumors along with the role of HSP70 protein in the prognosis of human breast cancer. A strong association between HSP70 expression and ER content, in agreement with previous data, was found which revealed a statistically significant association between HSP70 positivity and ER expression (p<0.008) in 50 cases of invasive primary human breast cancers. We also found a strong correlation between HSP70 expression, Grade and LNS of invasive ductal breast carcinomas. This suggests that the expression of HSP70 plays a significant role in the progression of human breast cancer, and might prove useful in many other malignancies as an important marker for the outcome of the disease.