After crossing Dnmt1Δ/Δ mice with MMTV-Neu-Tg mice, which mimic human luminal progenitor (LP) cell of origin, and C3 (1)-SV40-Tg, which mimic human basal triple-negative BC, results showed that Dnmt1-knockout remarkably suppressed cancer incidence, tumor size, and tumor sphere formation capacity. Here, DNMT1 is linked to neoplasm.