Role and prognostic significance of the Ki-67 index in non-Hodgkin's lymphoma

The Ki-67 monoclonal antibody recognizes a nuclear antigen that is present in all phases of the cell growth cycle but is absent in resting cells. The Ki-67 proliferation index is used to measure the growth fraction of malignant cells. In the major types of lymphoma, its range is very wide. Mean Ki-67 expression is low in indolent lymphomas and high in aggressive lymphomas; a cutoff index value of 45% can help clinicians to differentiate indolent from aggressive lymphoma. In follicular lymphoma, the Ki-67 proliferation index increases with increased follicular grade. In diffuse large B-cell lymphoma (DLBCL), most studies found that a high Ki-67 proliferation index (>60-70%) was a predictor of poor survival. The most extensive data exist on mantle cell lymphoma, for which multivariate analyses confirmed the central prognostic role of cell proliferation and the superiority of the Ki-67 proliferation index over all other histomorphological and clinical criteria. The stratification of patients with mantle cell lymphoma according to Ki-67 expression can be expected to have a profound impact on therapeutic options in risk-adapted strategies. For the prognostication of peripheral T-cell lymphoma, the Ki-67 proliferation index was integrated into a new predictive score. Thus, overall, the Ki-67 proliferation index is an important tool for determining lymphoma grade, and in many subtypes, it has prognostic significance. At the same time, it should be borne in mind that Ki-67 staining is still associated with poor reproducibility among laboratories, and each laboratory should determine its own cutoff values.