Expression of proliferating cell nuclear antigen in invasive ductal carcinoma of the breast.

Formalin-fixed, paraffin-embedded sections from 92 breast cancers (invasive ductal carcinomas) were immunostained with a monoclonal antibody against proliferating cell nuclear antigen (PCNA). The labeling index of PCNA ranged widely from 2 to 76 (mean 24.8)%. The labeling index was classified into three groups: low (< 25%), intermediate (25-50%), high proliferation (> 50%). Younger patients seemed to have a higher labeling index than older ones. The labeling index for tumors < or = 2 cm was lower than that of tumors larger than 2 cm. The labeling index in patients with high estrogen receptor (ER) levels (> 100 fmol/mg cytosol protein) was significantly lower than that in patients with low ER levels (< 10 fmol/mg cytosol protein). In relation to histological type, the labeling index of scirrhous carcinoma was significantly lower than that of papillotubular carcinoma or solid-tubular carcinoma. The high proliferating group had a significantly worse overall survival rate than the low proliferating group. Labeling index was shown to be a possible prognostic indicator.