A five-RNA model comprising Ala-CGC-2-1-tRF5D, SNORD116-4, snoRNA ACA64, miR-2467-5p, and piR-7447 could distinguish BC patients with ER+ from ER− tumors with an AUC of 0.924 (95% CI = 0.863–0.985, p = 9.2 × 10−5) on the training set and an AUC of 0.887 (95% CI = 0.809–0.966, p = 0.00038) in the LOOCV (Figure 5c,d). This evidence concerns the gene ESR1 and breast cancer.