IN-SITU ANALYSIS OF CELLULAR PROLIFERATION IN CANINE, FELINE AND EQUINE TUMORS BY IMMUNOHISTOCHEMISTRY - A COMPARISON OF BROMODEOXYURIDINE,PROLIFERATING CELL NUCLEAR ANTIGEN, AND INTERCHROMATIN-ASSOCIATED ANTIGEN IMMUNOSTAINING TECHNIQUES

Cell proliferation in canine, feline, and equine tumors was evaluated using immunohistochemical detection of in vitro 5-bromodeoxyuridine (B rdU) incorporation, proliferating cell nuclear antigen (PCNA), and int erchromatin-associated antigen (p105). Ten tumors in each species were analyzed. The tumor proliferative fraction (PF) was defined as the pe rcentage of labeled nuclei for 5,000 tumor nuclei counted. Immunoreact ivity was observed with all techniques in all species. A good correlat ion was observed between the proliferative fractions measured with the BrdU (PF(BrdU)) and PCNA (PF(PCNA)) techniques (r(s) = 0.523, P = 0.0 026). There was no correlation between the PFs measured with the BrdU (PF(BrdU)) and p105 (PF(P105)) techniques. Using the median values obt ained from the different approaches as cutoff points to define slowly and rapidly proliferating tumors, there was an 80% agreement (P = 0.00 9) between PF(BrdU) and PF(PCNA) and no agreement between PF(BrdU) and PF(P105). The results of this study indicate that both BrdU and PCNA labeling methods can be used reliably for identifying proliferating ce lls in animal tumors. In addition, PCNA could be used to replace the B rdU method to assess tumor proliferative fraction because it does not require pretreatment of tissues.