Ki-1-positive non-Hodgkin's lymphomas. An immunophenotypic, ultrastructural, and morphometric study.

The authors studied four cases of diffuse, large cell non-Hodgkin's lymphomas with strong Ki-1 expression to determine if they shared characteristic ultrastructural or morphometric features in common. The tumor cells in these lymphomas all had very abundant cytoplasm, which often showed a concentration of organelles, especially mitochondria and Golgi apparatus, in regions next to nuclear concavities. One case had very complex cytoplasmic membrane projections resembling a "microvillous" lymphoma. These ultrastructural features combined with the frequent reniform nuclei and scattered lysosomes suggested histiocyte differentiation. However the immunophenotype was variable, more often showing "activation" markers and abnormal T-cell marker patterns. The mean nuclear area for all cases was between 38.3 +/- 12.7 to 42.3 +/- 16.2 microns2, roughly twice the size of the small lymphocyte population. The nuclear contour index, a measure of irregularity of the nuclear membrane, ranged from 4.75 +/- 0.86 to 6.36 +/- 1.89 (a circle is 3.54). These nuclear parameters are comparable in size to those of previously measured large cell lymphomas but exhibit more nuclear irregularity than most. Ki-1 lymphomas appear to represent a somewhat diverse group of tumors of lymphoid origin that exhibit some hybrid features of histiocytes.