A second hallmark of CTCF-altered endometrial cancers is the upregulation of estrogen-responsive genes, which includes KIAA1324, MLPH, MSX2, SPDEF, TFF3 and PIGR. CTCF mutations do not occur in a tumour type-specific manner, but rather they define a subset of hormone-responsive cancers [31]. The gene discussed is TFF3; the disease is cancer.