1984 Volume 75 Issue 9 Pages 792-797
The clonal origin of spontaneous multiple mammary tumors in mice was examined. For this purpose, hybrid female mice (Pgk-1b/Pgk-1a), F1[SHN(Pgk-1b)×C3H/He (Pgk-1a)], with X-chromosome inactivation mosaicism with regard to the phosphoglycerate kinase (PGK)-1 isozyme together with a high incidence of spontaneous mammary tumors were constructed. Thirty-seven of 45 mammary tumors (82%) in mosaic mice had a single phenotype of PGK, indicating monoclonal origin. The multiple mammary tumors formed in these mice varied in PGK type, indicating independent cellular origins.