KI-S1, A NOVEL PROLIFERATIVE MARKER - FLOW CYTOMETRIC ASSESSMENT OF STAINING IN HUMAN BREAST-CARCINOMA CELLS

There is considerable interest in immunohistochemical markers of proliferation which are suitable for use on routinely fixed clinical material. The novel proliferation-associated antibody Ki-S1 shows promise in this respect. In this study we have: (i) defined the pattern of Ki-SI labelling relative to the cell cycle phase; (ii) investigated the labelling pattern with Ki-S1 on a human breast cell line (ZR75) under varying proliferative conditions induced by serum deprivation and refeeding; (iii) examined in a flow cytometric study Ki-S1 staining in archival, clinical breast carcinoma samples. In exponentially growing cells Ki-S1 showed a marked cell cycle phase-specific variation in staining intensity which increased linearly through the S-phase, was high in G2 and reached its peak in mitosis. Ki-S1 staining intensity mirrored the changes in proliferative activity of ZR75 cells during serum deprivation and refeeding. In a small series of human breast carcinomas, Ki-Sl staining intensity correlated with S-phase fraction (SPF) derived from DNA profiles. The antigen labelled by Ki-S1 is extremely robust, resisting degradation by fixation and by an aggressive enzymic tissue disaggregation method. Ki-S1 warrants further investigation as a proliferation-related marker, particularly for routine clinical application.