ESR1 and neoplasm: After the initial tumor was palpated in a second cohort (n=2) of Col1a1FRT-STOP-FRT-Cre-ER-T2; KrasFRT-STOP-FRT-G12D/+; p53FRT/FRT; Rosa26mTmG/+ mice, a single dose of 0.75 mg 4-hydroxytamoxifen in DMSO was delivered via intratumoral injection.