ESR1 and neoplasm: To examine the functionality of the Col1a1FRT-STOP-FRT-Cre-ER-T2 allele in a tumor model, these mice were crossed to KrasFRT-STOP-FRT-G12D/+; p53FRT/FRT; Rosa26mTmG/+ mice to generate Col1a1FRT-STOP-FRT-Cre-ER-T2; KrasFRT-STOP-FRT-G12D/+; p53FRT/FRT; Rosa26mTmG/+ mice.