Hormone Receptor and HER2 Testing Guidelines for Breast Cancer

1. Mandatory Biomarker Assessment

• All invasive breast cancers must have estrogen‑receptor (ER), progesterone‑receptor (PR), and HER2 status determined by immunohistochemistry (IHC) and/or in‑situ hybridization (ISH) because these are the only validated markers that directly guide treatment and affect mortality and quality of life. [1][2]3
• ER testing is required for every ductal carcinoma in situ (DCIS) and all invasive breast cancers. [1][2]4
• PR testing is required for all invasive breast cancers. [1][2]4
• HER2 testing is required for all newly diagnosed invasive breast cancers. [1][2][4][3]

2. Timing and Specimen Requirements

• A core‑needle biopsy must be performed before any therapy to confirm invasive disease and to obtain tissue for biomarker assessment. 3
• Biomarker testing should be carried out on the initial diagnostic specimen using proper fixation (e.g., neutral‑buffered formalin, ≤72 h) to preserve antigenicity. 3
• When disease recurs, biomarkers must be re‑tested on metastatic lesions because receptor status can change; discordance is reported in 9–12 % of cases. 5

3. Testing Methodology

3.1 ER and PR

• IHC is the standard method for ER and PR evaluation. [1][2]6
• Laboratories must validate their assays to achieve ≥90 % concordance for positive results and ≥95 % concordance for negative results compared with clinically validated reference methods. 6
• A tumor is considered ER/PR‑positive when ≥1 % of tumor cells show nuclear staining, per ASCO/CAP guidelines. 6
• Standardized scoring systems (Allred score or H‑score) should be applied to report results. 3

3.2 HER2

• Six FDA‑approved HER2 testing platforms are recognized:

 [1][2]4

• HER2‑positive criteria (ASCO‑CAP 2013 update):
  
  • IHC 3+ when >10 % of tumor cells display complete membrane staining. 3
  • FISH positive when HER2 gene copies ≥ 6 or HER2/CEP17 ratio ≥ 2.0. 3
• Equivocal HER2 results require reflex testing: IHC 2+ must be confirmed by FISH; FISH ratios 1.8–2.2 or gene copies 4–6 need an alternative method. [1][2]

4. Laboratory Quality and Accreditation

• Only laboratories accredited by recognized bodies (e.g., CAP, CLIA) should perform ER, PR, and HER2 testing. [1][2]
• Accredited labs must maintain standardized testing protocols and participate in proficiency‑testing programs. [1][2]
• Initial assay validation must demonstrate ≥95 % concordance with a clinically validated reference assay. [1][2]6
• Inter‑laboratory variability is a known issue; ER/PR reliability can differ widely among labs. [1][2]
• False‑positive and false‑negative HER2 results are common in routine practice, underscoring the need for strict quality controls. [1][2]

5. Clinical Decision‑Making Based on Biomarker Status

• ER/PR‑positive disease → eligibility for endocrine therapy (tamoxifen or aromatase inhibitors); endocrine therapy is first‑line for metastatic disease unless a visceral crisis is present. 5
• HER2‑positive disease → eligibility for HER2‑targeted agents (trastuzumab, pertuzumab, T‑DM1, lapatinib); metastatic HER2‑positive cancer requires dual HER2 blockade (trastuzumab + pertuzumab) combined with chemotherapy. 5
• Triple‑negative disease (ER‑/PR‑/HER2‑) → primary systemic treatment is chemotherapy; BRCA testing should be considered to identify candidates for PARP inhibitors. 3
• When primary tumor and metastatic lesion have discordant receptor status, therapy should be guided by the metastatic biomarker profile (ASCO consensus). 5

6. Pathology Reporting and Common Pitfalls

• Essential report elements: tumor site, specimen type, histologic type/grade, ER percentage, PR percentage, HER2 result (IHC score or FISH ratio/gene copies), fixation method and duration. [1][2]
• Up to 50 % of pathology reports omit one or more critical elements, potentially compromising treatment decisions. [1][2]
• Do not initiate therapy when any biomarker result is missing or equivocal without completing reflex testing. 5
• Always retest biomarkers on metastatic tissue; do not assume receptor status remains unchanged at recurrence. 5
• Non‑validated or non‑FDA‑approved assays should not be used for treatment decisions outside of clinical trials. 5
• If a core‑biopsy shows negative ER/PR/HER2, a repeat test on the surgical specimen is recommended to address possible tumor heterogeneity. 3
• Proper specimen orientation and clear communication between clinicians and pathologists regarding biomarker testing requests are essential for accurate results. [1][2]

Biomarkers in Breast Cancer Prognostication and Treatment

Key Biomarkers and Their Clinical Significance

• The American Society of Clinical Oncology (ASCO) recommends that biomarkers such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) are essential for determining prognosis and guiding treatment decisions in breast cancer, as they directly impact mortality and quality of life by determining eligibility for targeted therapies 7, 8
• ER, PR, and HER2 are the only biomarkers with demonstrated clinical validity for guiding treatment decisions in metastatic breast cancer, serving as both prognostic factors and predictive factors 8, 9
• ER and PR status determines eligibility for endocrine therapy, while HER2 status determines eligibility for anti-HER2 targeted therapies, according to the American College of Pathologists (ACP) and ASCO guidelines 9, 7

Testing and Interpretation

• The Food and Drug Administration (FDA)-approved testing methods for ER, PR, and HER2 include immunohistochemistry (IHC) for protein expression and in situ hybridization (ISH) for gene alterations, as recommended by the College of American Pathologists (CAP) and ASCO 7, 9
• Guidelines from ASCO/CAP provide standardized protocols for testing and interpretation, ensuring accurate and reliable results 7

Receptor Conversion and Retesting

• The ASCO panel recommends using the receptor status from the metastasis to direct therapy when discordance occurs between primary and metastatic tissues, taking into account the clinical scenario and patient's goals for care 7, 9

Biomarker-Guided Treatment Decisions

• In early-stage breast cancer, additional biomarker assays like Oncotype DX, EndoPredict, PAM50, and Breast Cancer Index have demonstrated clinical utility for guiding adjuvant systemic therapy decisions in specific subgroups, as recommended by the National Comprehensive Cancer Network (NCCN) 10, 11
• For ER+/PR+/HER2- node-negative breast cancer, the 21-gene recurrence score (Oncotype DX) may guide decisions on adjuvant chemotherapy, according to the American Society of Clinical Oncology (ASCO) 11, 12
• For metastatic disease, treatment decisions are primarily guided by ER, PR, and HER2 status, with ER+ metastatic disease typically treated with endocrine therapy and HER2+ disease treated with HER2-targeted therapies, as recommended by the European Society for Medical Oncology (ESMO) 8, 9

Clinical Pitfalls and Caveats

• Tumor heterogeneity may lead to sampling errors and discordant results, highlighting the importance of accurate testing and interpretation, as emphasized by the College of American Pathologists (CAP) 9
• While multiple biomarker tests are technically possible, only ER, PR, and HER2 have demonstrated clinical validity for treatment decisions outside clinical trials, according to the American Society of Clinical Oncology (ASCO) 8, 9