The literature on disease in lower animals offers very little information as to possible variations in resistance or susceptibility of different animal groups to the development of neoplasms. Observations on captive wild mammals and birds have indicated, however, that all taxonomic groups may not be equally affected and that there may be distinct differences in organ and tissue susceptibility to tumor growth.
A review (1) of the autopsy records of more than 5000 wild mammals and birds dying in the Philadelphia Zoological Gardens has shown that tumors occurred in about 2 per cent of all specimens. Mammals were much more frequently affected than were birds, although the latter were much more numerous in this series. The incidence of tumors also varied widely for different taxonomic groups (orders) of both mammals and birds.
The neoplasms found in these animals involved a variety of tissues, but the gastro-intestinal tract and related organs of mammals and the renal-adrenal-gonad tissues of birds, respectively, were more frequently the sites of tumor growth than other parts of the bodies. The skin of birds and the mucocutaneous junction of both birds and mammals were rarely affected by neoplasms.
The present report is a second survey of all cases of tumors that have been found in wild birds and mammals dying in the Philadelphia Zoological Gardens from 1901 to 1932.2 Those instances discussed in earlier publications (1, 2) have been reexamined and included in the present discussion.
Read before the American Association for Cancer Research, Philadelphia, April 1932.