Clonal origin of spontaneous multiple mammary tumors in mice with cellular mosaicism

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) X 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.