RNAseq datasets were generated from the August-Copenhagen-Irish (ACI) rat model of breast cancer. Rats were implanted with placebo or 7.5 mg E2 pellets to induce mammary tumorigenesis, and then left untreated or treated with 15 mg/ml of lamivudine (3TC) in drinking water for 6 months. RNAs were isolated from breast tissue samples or PBMCs using the mirVana RNA kit (ThermoFisher, AM1560) and extensively treated with Turbo DNase (ThermoFisher, AM1907) to remove genomic DNA. RNAseq libraries were prepared with the SMARTerStranded Total RNA-Seq Kit v3 - Pico Input Mammalian formulation (634356) and the Takara SMARTer RNA unique Dual index kit  96U (634457) and paired-end sequenced on the Illumina NovaSeq 6000 sequencer.