Differences in tumor incidence in two substrains of Claude BALB/c (BALB/cfCd) mice, emphasizing renal, mammary, pancreatic, and synovial tumors.

Observations were made on the tumor incidences in two substrains of the BALB/CFCd mouse. A total of 900 mice were examined. They comprised two substrains (families), direct descendants of two different females (designated 916 and 917) of the 31st inbred generation. Offspring of sibling matings of the fourth and fifth generation descendants of these two females were killed when moribund or when they had visible or palpable masses. Complete gross and microscopic examinations were conducted. Renal tumors were noted in 48.1% of those necropsied in family 916 and in 24.6% of those in family 917 (p less than .025). Mammary tumors were found in 13.3% of family 917 and in 3.3% of family 916 (p less than .001). Neoplasms of the reticulo-endothelial system (reticulum cell neoplasms, lymphocytic leukemia, other lymphocytic neoplasms) were found in 20.0% of family 917 but only in 11.2% of family 916 (p less than .005). Tumors of the respiratory system (primarily alveolar adenomas and alveolar adenocarcinomas) were found in 10.2% of family 916 and 16.5% of family 917 (p less than .05). Less commonly observed tumors included synoviomas, 7.6% in family 916 versus 2.1% in 917 (p less than .005), and seven pancreatic acinar adenomas, all but one of which were found in family 916. Also recorded were a total of nine myoepitheliomas, 28 hemangioendotheliomas, two interstitial cell tumors of the testis, a single mesothelioma and a single rhabdomyosarcoma of the esophagus. Degenerative lesions consisting of kyphoscoliosis were noted in 3.7% of mice examined in both families combined.