For other APOBEC family members (Additional file 2: Figure S1), they show either extremely low (median log2-transformed RPKM < 0) mRNA levels (including APOBEC3A, APOBEC3H, APOBEC1, APOBEC2, APOBEC4, and AICDA), or no obvious expression differences between ER+ and ER− breast cancers (including APOBEC3D, APOBEC3F, and APOBEC3G). The gene discussed is APOBEC4; the disease is breast cancer.