RT-PCR analysis revealed that SPAG9 mRNA was found in all breast cancer cell line models used in the present study [MCF-7 (ER+/PR+/Her2- luminal-A subtype), SK-BR-3 (ER-/PR-/Her2+ ERBB2 associated subtype), BT-474 (ER+/PR+/Her2+ triple-positive luminal-B subtype) and MDA-MB-231 (ER-/PR-/Her2- triple-negative basal subtype)] as shown in Figure 1a. This evidence concerns the gene ESR1 and breast cancer.