The majority of research to date is in breast cancer, where MASTL overexpression correlates significantly with increased chromosome instability, mitotic index, nuclear pleomorphism, histological grade and poor overall survival, (Álvarez-Fernández et al., 2018; Rogers et al., 2018; Yoon et al., 2018), and with a high risk of metastatic relapse in estrogen receptor (ER) positive patients (Zhuge et al., 2017). The gene discussed is ESR1; the disease is breast cancer.