What is a Breast Panel?
A "breast panel" refers to the comprehensive set of biomarker tests performed on breast tissue specimens to determine tumor hormone receptor status (estrogen receptor/progesterone receptor [ER/PR]) and HER2 status, which are essential for guiding treatment decisions in breast cancer. 1
Core Components of the Breast Panel
The breast panel includes testing for three critical biomarkers:
- Estrogen Receptor (ER) status - determines if the tumor responds to estrogen and predicts response to endocrine therapy 1
- Progesterone Receptor (PR) status - provides additional information about hormone sensitivity and treatment response 1
- HER2 status - identifies tumors that overexpress HER2 protein, which predicts response to HER2-targeted therapies like trastuzumab 1
When the Breast Panel is Performed
All patients with newly diagnosed invasive breast cancer must have determination of ER/PR and HER2 status as part of their initial pathologic assessment. 1
The panel is performed on tissue obtained from:
- Core needle biopsy of the primary breast tumor (preferred initial method) 1
- Surgical excision specimens if core biopsy was not performed 1
- Lymph node biopsies when metastatic disease is present 1
Clinical Significance
These biomarkers are not merely prognostic—they are predictive factors that directly determine treatment selection:
- ER/PR-positive tumors (approximately 70% of breast cancers) are treated with endocrine therapy (tamoxifen, aromatase inhibitors) 1
- HER2-positive tumors (approximately 15-20% of breast cancers) receive HER2-targeted therapy such as trastuzumab or pertuzumab 1
- Triple-negative tumors (ER-negative, PR-negative, HER2-negative) require chemotherapy as the primary systemic treatment 1
Standardized Reporting Requirements
The College of American Pathologists (CAP) protocols must be used for all breast cancer pathology reporting, including the breast panel results. 1
This standardization is critical because:
- National surveys show up to 50% of breast cancer pathology reports are missing critical elements needed for treatment decisions 1
- Incomplete reporting can lead to inappropriate treatment selection and worse outcomes 1
- The CAP protocols ensure consistent, complete documentation of all biomarkers 1
Common Pitfalls to Avoid
- Failing to test all three markers - some providers may omit PR testing if ER is positive, but PR status provides independent prognostic information 1
- Not obtaining adequate tissue - insufficient tissue from fine-needle aspiration may preclude complete biomarker testing; core biopsy is preferred 1
- Delaying treatment while awaiting results - the breast panel should be ordered immediately upon diagnosis, as results typically take 3-5 days and are required before initiating systemic therapy 1