GROWTH FRACTIONS IN CANINE NON-HODGKINS-LYMPHOMAS AS DETERMINED IN-SITU BY THE EXPRESSION OF THE KI-67 ANTIGEN

The proportion of proliferating cells in non-Hodgkin's lymphomas (NHLs ) as determined in situ by the expression of the Ki-67 antigen, has pr ognostic value in human oncology, and is strongly related to the diffe rent grades of malignancy. The evaluation of the Ki-67 index in canine NHLs may be useful in assessing the individual variability of the gro wth fraction in the different sub-types of lymphoma, and also the vali dity or the classification in terms of grade of malignancy. The growth fraction was evaluated in 92 canine NHLs, previously classified accor ding to the Kiel classification (as adapted to the canine species), by determining the expression of the Ki-67 antigen with the MIB1 antibod y on (1) paraffin-wax tissue sections in all 92 cases, and (2) fine-ne edle aspirates or tumour imprints in 30 cases. The labelling appeared satisfactory in 88% of the cases, with good concordance between the hi stological and cytological data. A highly significant correlation (P<0 .001) was established between the proportion of Ki-67(+) cells and the classification into low-grade (Ki-67 index <21%) and high-grade malig nancy (Ki-67 index >21% and usually >29%). In the low-grade lymphoma g roup, a macronucleolated medium-sized-cell lymphoma not found in man b ad the lowest proliferation index. In the high-grade malignancy group, the number of Ki-67(+) cells seemed to be proportional to cell size, whatever the phenotype, with the rare exceptions of some unclassifiabl e small cell Burkitt-type or plasmacytoid lymphomas, which were highly proliferating. The classification of lymphomas into low-grade and hig h-grade appears to correlate well with their proliferative index. The existence of individual variations, within given categories of canine NHL, suggests that, as in human medicine, prognosis may be assisted by determining the growth fraction at initial diagnosis, and by fine-nee dle aspiration at relapses. (C) 1997 W.B. Saunders Company Limited.