PGR and in situ carcinoma: In our study, carcinoma in situ had the highest and medullary carcinoma the lowest frequency of PR expression, which might suggest that in situ carcinomas progress very slowly under hormone suppression therapy and it might even be possible to prevent them from becoming invasive over time.4 In a study conducted by Bae et al,16 however, the highest frequency of PR expression pertained to mucinous carcinoma.