ESR1 and breast cancer: We performed large-scale comparison of single nucleotide variation (SNV) differences between three breast cancer subtypes (ER+ vs. ER-, PR+ vs. PR-, HER2+ vs. HER2-), two different histologic grades (grade II vs. grade III), and two different stages (stage II vs. stage III), all of which are clinical features that are directly associated with prognosis of breast cancers.