When SphK1 isoform expression status was considered by breast cancer grade (Table 3) and by hormonal status (ER+ or ER−) (Table 4), we found that most of Grade 1, 2, IDC, and ILC tissue resections had undetectable levels of SphK1b isoform, whereas all Grade 3 breast tissues proved positive for SphK1b expression (Table 4). This evidence concerns the gene ESR1 and breast cancer.