Proliferating cell nuclear antigen in benign breast diseases.

The expression of PCNA was examined by immunohistochemistry on 95 formalin-fixed breast surgical specimens. Seventy-four were benign breast disease, 3 atypical hyperplasia; 5 in situ carcinoma; 13 invasive carcinoma. Forty-two percent of benign breast disease, 75% of atypical hyperplasia/in situ carcinoma and 92% of invasive breast carcinoma expressed PCNA nuclear staining. Forty percent of cysts, 15.78% of sclerosing adenosis, 22.22% of adenosis, and 17.39% of epitheliosis expressed low cyclin protein levels (PCNA score I, < 18%); 20% of cysts, 31.57% of sclerosing adenosis, 5.55% of adenosis and 43.47% of epitheliosis expressed moderate levels (PCNA score II, 18 to 50%); whereas 50% of atypical hyperplasia/in situ carcinoma and 54% of invasive breast carcinoma contained high levels (PCNA score III, > 50%). This study on PCNA/cyclin localization suggests that PCNA is an early indicator of ongoing cellular proliferation.