ERpositive

ER-positive, short for estrogen receptor positive, describes tumor cells that express estrogen receptor alpha (ERα). The most common context is breast cancer, where ER positivity indicates that estrogen signaling can drive tumor growth. ER status is typically determined by immunohistochemistry on biopsy or surgical specimens and is used to guide therapy.

Assessment and thresholds: ER status is measured by IHC, reporting the percentage of tumor cells with nuclear ER staining and the staining intensity. A commonly used threshold for positivity is 1% or more of tumor cells staining for ER, though scoring schemes such as the Allred score (0-8) or H-score provide more detail about proportion and intensity. ER expression can be heterogeneous within a tumor, and different areas may show varying levels of positivity.

Clinical significance: ER-positive tumors are frequently classified as luminal subtypes and tend to grow more slowly than ER-negative cancers. They generally have a better short-term prognosis and are more likely to respond to endocrine therapies. However, there is a risk of late relapse, particularly after five to ten years, necessitating long-term follow-up and sometimes extended therapy.

Treatment and management: In early-stage ER-positive breast cancer, endocrine therapy is central. Premenopausal patients commonly receive tamoxifen, while postmenopausal patients receive aromatase inhibitors; ovarian suppression may be added for certain premenopausal patients. Adjuvant therapy usually lasts five to ten years. In metastatic disease, endocrine therapy remains first-line; if progression occurs, options include switching to another hormonal agent or combining with targeted therapies such as CDK4/6 inhibitors (palbociclib, ribociclib, abemaciclib), everolimus with exemestane, or alpelisib for PIK3CA-mutant tumors, or fulvestrant.

Notes: ER status is analyzed alongside PR and HER2 to define subtypes and guide treatment. While the term ER-positive is most common in breast cancer, expression concepts and thresholds can vary by cancer type and assay.