Conversion disorder.

Breast cancer metastases can change their receptors quite frequently. The estrogen receptor (ER) is lost in 223% of mets arising from ER(+) primaries, the progesterone receptor (PR) is lost in 49%, and HER2 in 21%. Conversely, ER is gained in 22% of mets arising from ER(-) primaries, PR is gained in 16%, and HER2 in 10%. Primary-metastasis ER discordance was particularly notable in brain and bone metastases. All this provides a strong argument to recheck receptor status on metastatic disease to ensure you’re implementing the best treatment for the disease at hand.