ESR1 and breast cancer: H19 expression was assessed using qRT-PCR in MCF-7 (estrogen receptor positive: ER+) breast cancer cells treated with Doxorubicin (a DNA intercalating agent and potent Topoisomerase II inhibitor used to induce DNA double-strand breaks) or PARPis (Figure 1B), and increased H19 expression was observed in the Doxorubicin or PARPi-treated group.