Spontaneous Tumors in Holtzman-Source Rats of Various Ages

Abstract

Spontaneous development of tumors in 5086 Holtzman-source rats ranging in age from 1 to 18 months is reviewed. Overall incidence of tumors was 4.3% (8.2% for females, 2.3% for males). Statistical analysis of the data demonstrated that the potentiality for tumors was comparable to previously reported lifetime studies. Characteristics of development of tumors are given, and the more uncommon tumors are described briefly. The occurrence of tumors in young rats in this survey indicates the need for accumulating data on tumors in other than “old” rats as an aid in interpreting data obtained from toxicological studies.