Ki-1 -Positive Non-Hodgkin's Lymphomas: An Immunophenotypic, Ultrastructural, and Morphometric Study

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Abstract
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 Tcell marker patterns. The mean nuclear area for all cases was between 38.3 ± 12.7 to 42.3 ± 16.2 μm2, 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.