In summary, we have compared the usefulness of the ER/PR/HER2 subtyping of breast cancer with an IHC surrogate classification and, while both are valuable at categorizing breast cancer patients for survival purposes, the ER/PR/HER2 subtype is simple, inexpensive, easy to interpret, reliable, reproducible, and readily available for clinicians without additional tests. Here, ESR1 is linked to breast cancer.