pS2 protein and steroid hormone receptors in invasive breast carcinomas.

We have used immunohistochemical and hormone-binding techniques to determine the presence of estrogen receptors, estrogen-receptor protein, progesterone receptors and pS2 protein in 97 invasive breast cancers. Our group of tumors displayed the same frequency of estrogen receptors and progesterone receptors as other comparable groups, but it contained more tumors containing pS2 protein. We also observed staining of morphologically normal cells in lobules adjacent to the tumors and in several fibroadenomas; both findings vary from some other reports. We attribute these variations to the use of a sensitive immunohistochemical method and choice of the lowest possible threshold to classify a tumor as pS2-positive. If we used a higher threshold, then about 95% of the tumors containing pS2 protein also contained estrogen receptor protein. Our results add further weight to the assertion that tumors containing pS2 protein also display estrogen receptors. The data also provide theoretical and indirect support to the clinical prediction that tumors containing pS2 protein are more likely to respond to hormonal therapy and may have a more indolent course than tumors lacking the molecule.