A new retrospective study has reported that the hormone receptor status changes during tumor progression in nearly one-third of breast cancer patients. The study was designed to investigate the frequency of differences in estrogen receptor (ER) and progesterone receptor (PR) status between primary breast cancer tumors and metastases in patients who relapsed. Such differences are known as discordance. Treatment of stage IV breast cancer often is based on the primary tumor's characteristics, including ER and PR expression. However, hormone receptor discordance between the primary and subsequent tumors, if detected, could lead to different treatment. The study included breast cancers from patients in Stockholm that relapsed during the period 1997 to 2007. ER status was available for 486 patients concerning both the primary tumor and one or more recurrent sites. Similarly, PR status was available for 456 patients from the primary tumor and one or more recurrent sites. This resulted in a total of 679 ER pairs and 630 PR pairs.

In the case of ER, 27% of the patients were found to have changed from ER+ in the primary tumor to ER- in a relapse tumor; 8% changed from ER- to ER+. PR status was found to change in 38% of patients from PR+ to PR-; 5% changed from PR- to PR+. The ER groups (ER+ primary —> ER+ metastasis, ER- —> ER-, ER+ —> ER-, and ER- —> ER+), were found to have significantly different overall survival. In particular, survival was worse for those with metastases that were ER- compared to ER+, independent of the primary tumor's ER status. The authors conclude that since the hormone receptor status can change during cancer progression and since the ER status of metastatic sites influences survival, management of metastatic disease is not optimum when based on original tumor characteristics. Therefore, altered management through tumor progression may improve survival.