SPONTANEOUS LESIONS IN AGING FVB N MICE

The FVB/N mouse strain was created in the early 1970s and has since be en used extensively in transgenic research because of its well-defined inbred background, superior reproductive performance, and prominent p ronuclei of fertilized zygotes, which facilitate microinjection of DNA . Little is known, however, about the survivability and spontaneous di sease of nontransgenic FVB/N mice. Therefore, the purpose of this stud y was to determine survival to 24 mo of age and the incidence of neopl astic and nonneoplastic disease at 14 and 24 mo of age. At 14 mo of ag e, the incidence of tumor-bearing mice was 13% in males (n = 45) and 2 6% in females (n = 98). All tumors in males and most in females at thi s time were alveolar-bronchiolar (AB) neoplasms of the lung. Survival to 24 mo of age was approximately 60% in both sexes (29/50 males, 71/1 16 females), and the incidence of mice with tumors at this time was 55 % in males and 66% in females. In decreasing order of frequency, the f ollowing neoplasms were observed in >5% of subjects: in males, lung AB tumors, liver hepatocellular tumors, subcutis neural crest tumors, an d Harderian gland adenomas; in females, lung AB tumors, pituitary glan d adenomas, ovarian tumors (combined types), lymphomas, histiocytic sa rcomas, Harderian gland adenomas, and pheochromocytomas. Compared with other mouse strains, the observed incidences of tumors in FVB/N mice suggest a higher than usual rate of lung tumors and a lower than usual incidence of liver tumors and lymphomas. This tumor profile should be considered in the interpretation of neoplastic phenotypes in FVB/N-de rived transgenic lines.