Centrocytic lymphoma: a morphometric study with comparison to other small cleaved follicular center cell lymphomas and genotypic correlates.

Centrocytic lymphoma (ML,CC) is distinguished from other cleaved follicular center cell (FCC) lymphomas in the Kiel classification by the lack of noncleaved FCC and not by morphological differences between the centrocytes (cleaved cells). Immunophenotypic and genotypic studies, however, have shown that the centrocytes in ML,CC are distinct from those of other small cleaved FCC lymphomas (ML,FCC,SC). To morphologically compare the cells of ML,CC with nine previously studied ML,FCC,SC and to relate the findings in ML,CC to the varied descriptions of lymphomas of intermediate differentiation, a morphometric analysis of 22 ML,CC was performed. Nuclei in ML,CC were, on average, significantly larger, rounder, and had less frequent nucleoli than those in ML,FCC,SC; however, the proportion of small round lymphocytes did not differ. Among the ML,CC, the only apparent immunophenotypic/genotypic correlate that was identified was greater nuclear ellipticity for the biopsies lacking chromosome 11q13 bcl-1 or PRAD1 rearrangement. Repeat biopsies in four patients with ML,CC showed an increase in nuclear size. These data demonstrate that a lack of transformed cells is not the only morphological difference between ML,CC and ML,FCC,SC. The morphological distinction, however, is not based on the proportion of small round lymphocytes present. In addition, the morphometric parameters illustrate the nuclear variability among ML,CC and demonstrate how the disease may evolve over time.