A) MCF7-ESR1Y537S cells were grafted intravenously (tail vein), and mice were treated with placebo or Fulv. Metastatic burden was measured using IVIS to detect bioluminescence. N=6, metastatic tumor luciferase signal from each mouse is plotted. No statistically significant difference was detected in metastatic burden with Fulv using a two-way ANOVA for Fulv effect over time. B) Imaging of luciferase signal indicating metastatic outgrowth in the livers, lungs, and bones. C) RNA was isolated from the MCF7-ESR1Y537S xenograft liver tumors. mRNA expression of ERα target genes GREB1 and PgR, and cell cycle-related genes PCNA and Ki67 were measured by qRT-PCR. Unpaired t-test, p values are indicated. D) UMAP plots of Visium spots from 2 Veh and 2 Fulv tumors. UMAP plots E) 17 clusters were identified F) Level of total and specific human transcripts identified in xenograft tumors