Exposure to dim LAN induced a circadian disruption of nocturnal melatonin in nude rats bearing estrogen receptor alpha-positive MCF-7 human breast cancer xenografts and consequently, a complete loss of tumor sensitivity to doxorubicin, indicating that chemotherapy resistance might be due to a disruption of the circadian structure ultimately leading to low levels of melatonin at night [56]. The gene discussed is ESR1; the disease is breast cancer.