The Simpson index was shown to reflect the ITH of estrogen receptor (ER) and predicted patient prognosis,16 while Shannon entropy was associated with shorter BC-specific survival (BCSS) and disease-free survival in early-stage ER-positive and human epidermal growth factor 2 (HER2)–negative (ER+/HER2–) BC.10 This evidence concerns the gene ESR1 and breast cancer.