Occurrence of Tumors in Wild House Mice

Abstract

The occurrence of spontaneous tumors in wild house mice (Mus musculus) raised in captivity is recorded. All tumors included herein were visible on gross examination. A total of 225 mice was necropsied, of which 98, or 43.5 percent, had developed tumors. A total of 121 tumors was found, of which 44, or 36 percent, were in 107 mice from 2 to 24 months of age, and 77, or 64 percent, were in 118 mice from 25 to 33 months of age. Incidences of the most frequent tumors found were: pulmonary, 21 percent; reticulum-cell (type B), 10 percent; granulosa-cell of ovary, 5 percent; hepatomas, 5 percent; hemangioendotheliomas, 4 percent. Ninety-nine breeding females showed a mammary-tumor incidence of 6 percent; no mammary tumors were found in 72 nonbreeding females. Only 2 unquestionable lymphocytic neoplasms were found. One arose subcutaneously in the dorsal cervical region, and the other was in the thymus gland and was spreading beyond the capsule.