ANALYSIS OF DNA ANEUPLOIDY AND C-MYC ONCOPROTEIN CONTENT OF CANINE PLASMA-CELL TUMORS USING FLOW-CYTOMETRY

To derive a method for determining malignant potential of plasma cell tumors, a retrospective analysis of the DNA ploidy and relative p62(c- myc) oncoprotein content using bivariate flow cytometry was performed on 23 formalin-fixed, paraffin-embedded tissues from 23 dogs. The samp les included one tissue each from 17 males and six females 2 to 16 yea rs of age (mean = 7.5 years). Twelve breeds were represented, includin g three Cocker Spaniels, three Golden Retrievers, and live of mixed br eed. Ten of the samples were histologically classified as malignant-pl asma cell tumors, and ten specimens were classified as benign. Three s amples of plasmacytic inflammation, from two Cocker Spaniels and one S hih Tsu, were included as controls. The ploidy and relative c-myc cont ent data obtained were compared with the histologic grade. A significa nt difference in ploidy was found between benign and malignant tumors (P less than or equal to 0.05). Five of nine malignant plasma cell tum ors were aneuploid; the remainder were diploid (4/9) or tetraploid (1/ 9). Only one of the benign plasmacytomas was aneuploid (1/10), whereas six were diploid (6/10), and three were tetraploid (3/10). All of the controls were diploid (3/32). When relative amounts of p62(c-myc) fro m malignant and benign tumors were compared by flow cytometry, a great er significant difference was established (P less than or equal to 0.0 1) than by using aneuploidy alone. Relative values of p62(c-myc) conte nt ranged from 219 to 553 units in 8/10 malignant plasma cell tumors a nd from 86 to 392 units in 3/10 benign plasmacytomas. The remainder of the neoplasms (2/10 malignant and 7/10 benign) lacked measurable valu es of p62(c-myc) above background fluorescence concentrations. Two aty pical cutaneous plasmacytomas with later metastasis were included in t he study. The results indicate that simultaneous analysis of ploidy an d relative p62(c-myc) concentration can be used as an aid in assessmen t of malignant potential in canine plasma cell tumors.