ESR1 and cancer: While ESR1 binding was highly prevalent in L1 transposons of various evolutionary ages, the youngest L1 subfamilies (L1HS, L1PA2 and L1PA3) displayed a distinct TF binding repertoire compared to the more ancient L1 subfamilies (L1PA4-L1PA12), where the youngest subfamilies were frequently bound by cancer-associated TFs, including MYC, FOXA1 and E2F1, as well as the nuclear receptor NR2F2 and chromatin remodelling-associated CTCF (Figure 2).