Multiple primary tumors in domestic animals: a preliminary view with particular emphasis on tumors in dogs.

Cattle, horses, cats, and dogs with microscopically confirmed multiple primary tumors were reported to the Veterinary Medical Data Program, a system to collect, store and retrieve veterinary clinical information. Of 2611 tumors diagnosed prior to, concurrent with, or subsequent to other tumors during the period studied, 2361 were in 1062 dogs and 250 were in 120 other animals in all other species categories. The 604 multiple primary malignancies (two or more malignant tumors in one animal) were similarly distributed, by species, with 512 in dogs and 92 in all other species combined. The total number of multiple tumors reported in dogs closely approximated a theoretic model of random distribution, but several site-pairs of tumors seemed to occur excessively; one pair (mammary tumors and tumors of internal female organs) might parallel a similar excessive occurrence in women, suggesting a possible spontaneous tumor model for the latter.