The gene truncations we report in endometrial carcinoma disrupt the hormone-binding domain encoding sequence of ESR1. Similarly, mRNA splice variants lacking one or more of exons 5–8, encoding the hormone-binding domain, have been described in normal35, 36, 37, 38 and malignant22, 23, 35, 36, 37, 39 breast as well as in normal22, 40, 41, 42, 43, 44, 45 and malignant42, 43, 44, 45, 46 endometrial tissue. The gene discussed is ESR1; the disease is endometrial carcinoma.