Prognostic significance of a formalin-resistant nuclear proliferation antigen in mammary carcinomas as determined by the monoclonal antibody Ki-S1.

Proliferative activity is a potential prognostic indicator of neoplastic cell growth. Usually the assessment of the tumor growth fraction requires specially processed or frozen tissue. We have raised a monoclonal antibody, Ki-S1, suitable for the detection of proliferating cells in routinely processed and paraffin-embedded tissue specimens. A retrospective study was conducted on 83 mammary carcinoma patients with a median follow-up of 45.6 months. Ki-S1 positivity was significantly (P < 0.0001) correlated with the S-phase fraction. A high proliferative activity of more than 30% of tumor cells being Ki-S1-positive was significantly correlated with recurrence (P < 0.001). Cumulative survival was significantly reduced in the high Ki-S1 expressing subgroup. In a multivariate model including Ki-S1, lymph node metastases, tumor size, and progesterone receptor positivity, independent significant information was provided by Ki-S1. We conclude that in mammary carcinomas, Ki-S1-determined growth fraction represents a significant and independent prognostic predictor.