ESR1 and breast cancer: The lowest frequency of ER and PR expression is related to the medullary carcinomas, which is consistent with findings of other studies.4,14 In a study conducted by Li et al15 on the hormonal status of patients with breast cancer, the highest frequency of ER expression pertained to mucinous and invasive lobular carcinomas, which was inconsistent with the findings of the present study in which mucinous carcinomas had a lower frequency of ER expression compared with lobular carcinomas.