ERHER2

ERHER2 is not a separate gene or protein. In many scientific discussions, it is used as a shorthand to describe tumors that express both estrogen receptor (ER) and human epidermal growth factor receptor 2 (HER2). The term is most commonly encountered in the context of breast cancer, where dual positivity for ER and HER2 defines a distinct phenotype within the disease.

Prevalence and relevance vary by population, but ER-positive/HER2-positive tumors represent a subset of breast cancers and are typically a minority of all cases. The exact proportion depends on cohort characteristics and testing practices.

Diagnosis and testing rely on standard pathology methods. ER status is determined by immunohistochemistry (IHC) with a positive result usually defined by a certain percentage of tumor cells showing nuclear staining. HER2 status is initially assessed by IHC and is further refined by in situ hybridization (FISH or similar) when IHC results are equivocal. Accurate determination of both ER and HER2 status is essential for guiding therapy.

Biology and treatment considerations reflect cross-talk between ER and HER2 signaling pathways. HER2 signaling can influence estrogen signaling and contribute to resistance to endocrine therapy, while estrogen signaling can modulate HER2 activity. Consequently, management often employs combined targeting of both pathways.

Therapeutic implications include the use of endocrine therapies (such as aromatase inhibitors, tamoxifen, or fulvestrant) alongside HER2-directed therapies (such as trastuzumab and/or pertuzumab) and, in some regimens, chemotherapy. The approach is individualized based on disease stage, prior treatments, and patient factors.

Note: ERHER2 is a descriptive phenotype rather than a distinct gene; for gene-level references, see ESR1 and ERBB2 (HER2).