Minimal breast cancer: analysis of proliferative activity using a monoclonal antibody to proliferating cell nuclear antigen (PCNA) and its relationship to histological grade and prognosis.

Sixty-five cases of invasive breast cancer < or = 1 cm. in largest diameter (pT1a-b) were studied retrospectively using immunohistochemical staining with PC10, a monoclonal antibody to proliferating cell nuclear antigen (PCNA). The percentage of PC10 positive tumor cells was closely related to histological grading. No association was found between PC10 score and nodal status. ER-ICA was performed on 42 cases and showed no correlation with PC10 staining. The clinical behaviour of these tumors was excellent, with 5-year survival rates overall of 96% (90% disease free survival), and apparently unrelated to histological type and grade, nodal involvement and hormonal receptor status. The prognostic value of PCNA labeling rates remains nuclear in breast cancer of minimal size as well as in larger ones.