Y537S and D538G mutations were found in approximately 12.7% of the primary tumors analyzed in this study, and approximately 25% of ESR1 mutations of whole exons were present in the primary tumors, which is close to the frequency of ESR1 mutations reported for recurrent breast cancers (20–50%) [7,11,14,33,34,35]. This evidence concerns the gene ESR1 and breast cancer.