ER+ tumours had more PIK3CA mutations in codons 345 (62 out of 942 ER+, 2 out of 162 ER−; P=0.003396, Fisher's exact test) and codons 542 or 545 (helical domain; 259 out of 942 ER+, 32 out of 162 ER−; P=0.04245). The gene discussed is ESR1; the disease is neoplasm.