The pS2 gene, mRNA, and protein: a potential marker for human breast cancer.

Approximately 50% of human breast tumors secrete a small cysteine-rich protein called pS2. In the human breast cancer cell line MCF-7, expression of the pS2 protein is strongly induced by estrogen, and cloning and sequence analysis of the pS2 gene has revealed an "estrogen responsive element" in the gene's 5'-flanking region. The results of immunohistochemical assays and radioimmunoassays on breast cancer biopsies indicate that the pS2 protein is a marker for hormone-dependent breast tumors and that its expression is associated with longer overall, and disease-free, survival. The pS2 protein is also expressed in normal stomach mucosa and in regenerative tissues in ulcerative diseases of the gastrointestinal tract. Its physiological function is unknown.