Expression of the double-stranded RNA-dependent protein kinase (p68) in human breast tissues.

P68 is a potent inhibitor of protein synthesis in virally infected cells and has been suggested to function in noninfected cells as a tumor suppressor gene. We have previously demonstrated that p68 expression correlates directly with cellular differentiation and inversely with proliferative activity in normal epithelium and in several human tumor systems. In order to determine the role of p68 in human breast cancer, we utilized immunohistochemistry and mapped the expression of p68 in tissue from 200 breast biopsy specimens. A total of 434 foci, ranging from normal breast tissue to infiltrating carcinoma were examined. We found that p68 was present at basal levels in normal lobular and luminal ductal epithelial cells, with higher levels present in myoepithelial cells. Nonproliferative fibrocystic lesions showed variable expression of p68, with high levels seen within foci of apocrine metaplasia and low levels in cystically dilated terminal duct units. Low levels of p68 were seen in typical ductal proliferations, lobular neoplasia (atypical lobular hyperplasia and lobular carcinoma in situ), and in fibroadenomas. Foci of atypical ductal hyperplasia in situ and invasive ductal carcinoma generally showed higher levels of p68 expression. Among the infiltrating carcinomas, p68 expression correlated with nuclear grade. This suggests that the ability of p68 to inhibit cellular proliferation may be impaired in breast cancer and that its expression, although modestly paralleling cellular differentiation, is not a predictive indicator of improved survival.