A new study presented at the 2011 European Multidisciplinary Cancer Congress has reported that breast cancer patients can experience changes in receptor status throughout tumor progression. Currently, metastatic breast cancer patients are often treated based on their original tumor receptor status.

The study included breast cancer patients from the Stockholm area who relapsed between 1997 and 2007. The estrogen receptor (ER+), progesterone receptor (PR), and HER2/neu amplification (HER2) status of local, locoregional and distant relapses were determined. ER and PR status in 119 recurrence sites were assessed in 116 patients.

Receptor status was found to be unstable in a large minority of women, including during metastatic disease progression. A total of 33.6% of the patients had discordant ER status between different sites of relapse: 16.0% of patients changed from ER+ to ER-; 12.6% changed from ER- to ER+; and 5.0% changed ER status back and forth throughout tumor progression. On the other hand, 36.1% of the patients were ER+ stable and 30.3% were ER- stable. A total of 30.2% of the patients had discordant PR status between different sites of relapse: the majority (19.8%) changed from PR+ to PR- whereas 10.4% changed from PR- to PR+. 15% of the patients also had changes in HER2 status during the course of disease. The authors conclude that breast cancer patients alter hormone receptor status throughout tumor progression. While doing so will add complexity to clinical decisions, the results indicate a potential need to take biopsies during disease progression, including in the advanced setting, in order to optimize treatment decisions for the patient.