Prognostic factors other than the stage in BC are ER and PR status, HER2 overexpression, Ki-67 proliferation index, and tumor grade, which are defined as biological prognostic factors.9 In our study, Ki-67 index and the grade of the tumor could not be evaluated because of the missing data in more than 50% of the patients. The gene discussed is ESR1; the disease is neoplasm.