Estrogen receptor (ER) immunohistochemistry (IHC) is a technique used to assess the expression of the estrogen receptor in breast cancer tissues.

The estrogen receptor is a hormone receptor that, when expressed, indicates that the cancer may be responsive to hormone-driven growth signals. IHC staining for ER involves applying an antibody that binds to the estrogen receptor within the nucleus, which is then visualized using a chromogen.

The staining is scored based on the percentage of tumor cells showing nuclear staining and the intensity of the staining, which determines ER positivity. This scoring is critical for assessing eligibility for hormone therapies such as tamoxifen or aromatase inhibitors, which are effective in ER-positive breast cancers.

PAIKON for IHC ER testing is currently availible as RUO product for microscopic and whole slide images.