Estrogen receptor negative and progesterone receptor positive breast carcinomas-how frequent are they?

Estrogen receptor (ER) testing has become an important part of breast cancer reporting as the ER status is a predictor of hormonal treatment efficacy. Progesteron receptors (PR) are often tested in parallel, and the best response to hormonal manipulations can be expected in tumors positive for both receptors. The existence of breast cancers with an ER negative and PR positive phenotype is controversial. A series of cases with this phenotype were reevaluated to clarify the existence and the frequency of this entity. A total of 205/6587 (3.1%; range of the rate per department: 0.3-7.1%.) cases reported to have the ER-negative and PR-positive status by immunohistochemistry were collected from 9 Hungarian departments. After careful reevaluation of the tumor slides and control tissues with a 1% cut-off for positivity and restaining of the questionable cases, all but 1 of the reevaluable 182 cases changed their original phenotype. Most cases converted to dual positives (n = 124) or dual negatives (n = 31) or unassessable / questionable. ER-negative and PR-positive breast cancers are very rare if existing. Such a phenotype should prompt reassessment.