How much variability can you see in levels of ER/PR expression between the primary tumor and a metastasis to make you reconsider if it's a second primary?

Expression of estrogen, progesterone receptors can vary over time and between primary and metastatic sites in approximately 10-15% of cases based on literature. It can also be affected by technical aspects such as cold ischemia time, negative/positive controls used and pathologist interpretation of ...