Expression of the pS2 protein and correlation with estrogen receptor status in fine-needle aspirates from breast...

A series of 36 cases of breast carcinomas diagnosed by fine-needle aspiration were investigated for the presence of estrogen receptors (ER) and the estrogen-induced pS2 protein. Immunocytochemically ER could be demonstrated in 28 aspirates, whereas eight were negative. These eight were also negative for the pS2 protein. In addition three aspirates with a low score for ER and five with a high score for ER were found negative for pS2. Thus, of the 36 cases, 20 were found to express the pS2 protein. The presence of the pS2 protein in the tumor cells is believed to be a marker of a functional estrogen regulatory system and its demonstration may therefore predict clinical responsiveness to hormonal therapy.