Althought immunohistochemistry (IHC) is the “gold standard” to determine the surrogate markers ER and PR for breast cancer classification, several studies addressed limitations in IHC by shedding light on the discordance rates in scoring hormone receptor status with negative and false-positive rates in ER and PR statuses higher than 20% [32, 33]. The gene discussed is ESR1; the disease is breast carcinoma.