DETERMINATION OF THE GROWTH FRACTION IN NON-HODGKINS-LYMPHOMAS BY MONOCLONAL-ANTIBODY KI-S5 DIRECTED AGAINST A FORMALIN-RESISTANT EPITOPE OF THE KI-67 ANTIGEN

Relevant prognostic information can be added to the histological class ification of non-Hodgkin's lymphoma (NHL) by the determination of the growth fraction In unfixed fresh tissue samples the Ki-67 antigen has proven its utility as an operational marker of proliferative activity in NHL. We have generated a monoclonal antibody directed against a for malin-resistant epitope of the Ki-67 antigen, designated Ki-S5. The im munoreactivity of Ki-S5 is confined to the nuclei of proliferating cel ls and, unlike Ki-67, no cross-reactivity with cytoplasmic antigens of epithelial cells occurs. In 100 cases of different NHL types, paralle l staining of Ki-67 and Ki-S5 antigen yielded almost identical results in fresh tissues and fixed tissues, respectively (P < 0,00001; r = 0. 95). In some cases, the Ki-S5 labeling index exceeded that of Ki-67, most probably due to a partial degradation of the epitope recognized b y Ki-67 in frozen stored tissue samples. Significant differences in th e median Ki-S5 labeling index could be demonstrated between high grade (>50%) and low grade malignant NHL (less-than-or-equal-to 30%), altho ugh the proliferative activity varied to a considerable range within i dentical histological categories (P < 0.001). We conclude that Ki-S5 p rovides a reliable means to assess proliferation in Paraffin-embedded NHL specimens. Retrospecclinical outcome are thus rendered possible us ing archival routinely processed tissue samples.