Breast Cancer Biomarkers

Primary carcinoma of the breast is the most common type of breast malignancy. Breast cancer is diagnosed by breast biopsy or excision and is then subsequently staged. Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) biomarker testing is performed to establish hormone receptor status, which provides both prognostic and predictive value. Women with early-stage invasive breast cancer and known ER+/PR+/HER2- status may then benefit from prognostic biomarker panels that can provide information to guide decisions about adjuvant systemic therapy. Individuals considered to be at risk for hereditary cancer may also undergo testing for pathogenic variants (mutations) that are commonly associated with breast cancer, including variants in BRCA1 and BRCA2 genes.

Quick Answers for Clinicians

What is the definition of estrogen receptor (ER) and progesterone receptor (PR) positivity?

According to the most recent American Society of Clinical Oncology (ASCO) and College of American Pathologists (CAP) guideline, breast cancer tumors are considered estrogen receptor (ER) and/or progesterone receptor (PR) positive if ≥1% of tumor cell nuclei are immunoreactive. 

What is the definition of human epidermal growth factor receptor 2 (HER2) positivity? How is HER2 status determined?

There are currently two approved methods for determining human epidermal growth factor receptor 2 (HER2) status in breast cancer: immunohistochemistry (IHC) and in situ hybridization (ISH). Breast cancer tumors are considered HER2+ if they are assigned a score of 3+ by an IHC method or demonstrate HER2 gene amplification by an ISH method. 

Equivocal results by IHC (considered IHC 2+) should be resolved by reflex testing using the ISH method on the same specimen or repeating tests if a new specimen is available. Equivocal results by an ISH assay must be confirmed by reflex testing using IHC methodology on the same specimen or by repeating tests if a new specimen is available.  

When is gene expression signature testing useful in the management of breast cancer?

The results of gene expression signature testing may help a clinician determine if a patient would benefit from chemotherapy and may predict the likelihood of breast cancer recurrence. Oncotype DX, EndoPredict, and Prosigna are three representative multigene tests that are commercially available; refer to the Multiplexed Gene Expression Panels for Prognosis in Early Stage ER+ Breast Cancer table for more information.

Are serum biomarkers useful for screening or managing breast cancer?

Serum biomarkers are not currently recommended for breast cancer screening, but active investigations are ongoing.  All markers have low sensitivity and specificity when used in a screening setting. However, some markers (eg, cancer antigen [CA] 15-3 and CA 27.29) may be used for monitoring metastatic breast cancer.

Is circulating tumor cell testing recommended in early-stage breast cancer?

Circulating tumor cells (CTCs) are frequently detected in metastatic, late-stage breast cancer but are rarely detected in early-stage breast cancer. For this reason, the role of CTC testing in early-stage breast cancer is unclear.

In its most recent guideline, the American Society of Clinical Oncology (ASCO) indicates that CTC testing is not recommended in patients with early-stage invasive breast cancer to guide decisions about adjuvant systemic therapy.  The National Comprehensive Cancer Network (NCCN) acknowledges that CTC testing can provide prognostic information but fails to show predictive value and is therefore not recommended.  A recent metaanalysis suggests that CTCs have clinical validity as a prognostic marker and may provide useful information to clinicians and patients. However, CTC test results may not provide actionable information that impacts clinical outcome. 

Who should be considered for hereditary breast cancer genetic testing?

Any individual suspected of being at risk for hereditary cancer should be offered genetic counseling in order to select appropriate candidates for genetic testing.   Genetic testing should be considered in high-risk individuals when it would impact medical management of the tested individual and at-risk family members.  Genetic testing may involve single-gene testing for pathogenic variants (mutations) in genes such as BRCA1/2 or multigene panel testing for additional high- and moderate-penetrance genes associated with breast cancer. Genes such as BRCA1/2, ATM, CHEK2, PALB2, and TP53 might be included in such a panel. For more information, refer to Familial Risk (Hereditary) Genetic Testing.

Which markers are useful for monitoring metastatic breast cancer?

Circulating tumor markers, including cancer antigen (CA) 15-3, CA 27.29, and carcinoembryonic antigen (CEA), may be useful for monitoring metastatic breast cancer along with clinical evaluation to determine treatment response.  Single measurements of these markers are not informative; serial measurements are required, using the same marker sequentially. 

Indications for Testing

Individuals with malignant histology that is compatible with breast cancer should undergo disease staging, hormone receptor testing, and possible genetic evaluation for prognostic and therapeutic purposes.

Laboratory Testing

Diagnosis and Staging

Diagnosis is established by surgical pathology. Grading and staging are based on histologic features, lymph node involvement, and metastasis. Interpretive guidelines have changed over the years; clinicians are advised to consult the most recent societal statements for recommendations.

Biomarker Testing for Prognosis and Therapy Decisions

Prognosis and therapeutic decisions are determined using a combination of tumor features, including ER, PR, and HER2 (or ERBB2) status, and, when appropriate, gene expression panels.

Tumor Hormone Receptor Status Testing

ER and PR status should be determined in all patients with invasive breast cancers and breast cancer recurrences.   ER and PR expression are generally associated with improved outcomes when the patient is treated with an antiestrogen therapy.   ER status is used to determine if a patient should or should not receive adjuvant endocrine therapy. PR status appears to be prognostic and independent of ER, and high levels are generally associated with a favorable outcome. 

Human Epidermal Growth Factor Receptor 2 Status

HER2 status should be determined in all patients with invasive breast cancer and first recurrences of breast cancer.  HER2 overexpression confers an unfavorable prognosis in the absence of therapy in patients with pathologically node-positive and node-negative breast cancer.  Immunohistochemistry (IHC) or in situ hybridization (ISH) methods may be used in the initial evaluation; equivocal results by IHC should be resolved by reflex testing using the ISH method on the same specimen or repeating tests if a new specimen is available. Equivocal results by an ISH assay must be confirmed by reflex testing using IHC methodology on the same specimen or by repeating tests if a new specimen is available.  

Multiplexed Gene Expression Assays for Prognosis in Early-Stage, Estrogen Receptor-Positive Breast Cancer

The American Society of Clinical Oncology (ASCO) 2016 recommendations address prognostic biomarker panels that may be helpful in guiding decisions about adjuvant systemic therapy for women with early-stage invasive breast cancer and known ER+/PR+/HER2- status. The results of this testing may help a clinician determine if a patient would benefit from chemotherapy and may also predict the likelihood of breast cancer recurrence.   Oncotype DX, EndoPredict, and Prosigna are three representative multigene tests that are commercially available; specifics about these tests are detailed in the table below.

Multiplexed Gene Expression Panelsa for Prognosis in Early-Stage, ER+ Breast Cancer
Marker Description Indications for Use Recommended for HER2+ Breast Cancer Utility in Late Recurrence
Oncotype DX Breast Recurrence Score (Genomic Health) Measures expression of 21 genes (16 cancer-related genes and 5 reference genes) to quantify the risk of distant recurrence and the likelihood of chemotherapy benefit Use to guide decisions for adjuvant systemic chemotherapy No No
EndoPredict (Myriad Genetics) EPclin Risk Score algorithm integrates 12 gene molecular scores, tumor size, and nodal status to generate 10-yr breast cancer recurrence risk score Use to guide decisions for adjuvant systemic chemotherapy No Yes
Prosignab Breast Cancer Prognostic Gene Signature Assay (NanoString Technologies) Proprietary algorithm determines probability of distant recurrence within 10 yrs Use to guide decisions for adjuvant systemic chemotherapy in conjunction with other clinicopathologic variables No (U.S. only) Yes

aAll three tests are validated in stage N0 and N1 cancers.

bUsed for prognosis only in ER+ breast cancer in the United States under FDA regulations, but available for use in all breast cancer cases outside the U.S. Refer to www.prosigna.com  for more information.

FDA, U.S. Food and Drug Administration; NCCN, National Comprehensive Cancer Network

Sources: NCCN ; Harris ; Duffy ; Andre ; Ohnstad ; Dubsky 

Familial Risk (Hereditary) Genetic Testing

Up to 10% of all breast cancers are due to specific pathogenic variants (mutations) in single genes passed down in a family.  BRCA1 and BRCA2 are the best characterized and most prevalent breast cancer susceptibility genes, but others (eg, ATM, CDH1, CHEK2, NBN, NFI, PALB2, PTEN, STK11, and TP53) are also associated with an increased susceptibility to breast cancer. 

Major organizations agree that any individual considered to be at risk for hereditary cancer should be offered genetic counseling. The U.S. Preventive Services Task Force (USPSTF) recommends that primary care clinicians assess women with a personal or family history of breast, ovarian, tubal, or peritoneal cancer or who have an ancestry associated with pathogenic variants in the breast cancer susceptibility 1 and 2 (BRCA1/2) genes with an appropriate brief familial risk assessment tool. Women who screen positive should be offered genetic counseling, and if appropriate, BRCA1 and BRCA2 testing. Routine testing is not recommended in women whose personal or family history or ancestry is not associated with an increased risk. 

The NCCN’s most recent guidance  continues to expand the criteria for testing individuals with clinical suspicion for a hereditary cancer. Genetic testing is clinically indicated for individuals with any blood relative with a known pathogenic/likely pathogenic variant in a cancer susceptibility gene. Testing is also recommended for individuals with a personal/family history of breast, ovarian, pancreatic, and/or metastatic prostate cancer who meet additional specific criteria. Testing is also indicated for individuals who have a personal history of cancer or family history of cancer but with previous limited testing (eg, single-gene testing and/or absent deletion/duplication analysis) who are interested in pursuing multigene testing.

Testing may be considered in individuals with bilateral breast cancer that is first diagnosed between the ages of 50 and 65 years; unaffected individuals with Ashkenazi Jewish ancestry; and affected or unaffected individuals who otherwise do not meet any of the above criteria but have a 2.5-5% probability of having a BRCA1/2 pathogenic variant based on previous probability models (eg, Tyrer-Cuzick, BRCAPRO, Penn II).

According to the NCCN, there is low probability that testing will result in findings of documented clinical utility in women diagnosed with breast cancer who are older than 65 years and have no close relative with breast, ovarian, pancreatic, or prostate cancer, or in men diagnosed with localized prostate cancer with a Gleason score <7 and no close relative with breast, ovarian, pancreatic, or prostate cancer.

Refer to the Hereditary Cancer Testing Criteria in the NCCN guideline for the full criteria. 

Other Testing

Liquid biopsy and circulating tumor DNA (ctDNA) analysis in breast cancer are emerging areas of research interest, but are not currently recommended as part of the standard of care by societal guidelines.

Circulating tumor cell (CTC) counts are not recommended as standard of care by ASCO and NCCN.   A recent metaanalysis suggests that CTC testing has clinical validity as a prognostic marker and may provide useful information to clinicians and patients. However, CTC test results may not provide actionable information that impacts clinical outcome. 

Monitoring

Cancer antigen (CA) 15-3, CA 27.29, and carcinoembryonic antigen (CEA) may be used to monitor metastatic disease in conjunction with diagnostic imaging, history, and physical examination.  Single measurements are uninformative; instead, serial measurements are required, using the same marker sequentially.  Increasing values of these markers can raise concerns about tumor progression, but may also be seen in the setting of responding disease.

The most recent NCCN guidelines  do not include recommendations regarding detection of CTCs in the management of patients with breast cancer. ASCO recommends that clinicians not use CTC testing to guide decisions about adjuvant systemic therapy. 

Pharmacogenetics

Many pharmacogenes are associated with drug response and optimal dosing. For example, the drug metabolizing enzyme encoded by CYP2D6 is involved in the conversion of tamoxifen, an antiestrogen drug used in the treatment of ER+ breast cancer, to the active metabolite endoxifen. Neither the NCCN nor ASCO recommend CYP2D6 genotyping to determine the optimal adjuvant endocrine strategy.   However, gene-based dosing guidelines are available for tamoxifen and many other drugs commonly used in treating patients with breast cancer through the Clinical Pharmacogenetics Implementation Consortium and the Dutch Pharmacogenomics Working Group.  In addition to the gene-based dose guidelines, it is important to be aware of common drug-drug interactions. For example, patients who are prescribed tamoxifen should avoid strong CYP2D6 inhibitors, such as most antidepressant drugs.

Refer to the ARUP Consult Germline Pharmacogenetics topic for more information on pharmacogenetics, and the ARUP Laboratories test directory for access to the complete menu of pharmacogenetic tests available at ARUP.

ARUP Laboratory Tests

ER and PR Testing

Prognostic and predictive testing

HER2 Testing

Prognostic and predictive testing

Includes reflex testing in case of equivocal result

Prognostic and predictive testing

Alternate test to confirm equivocal fluorescence in situ hybridization (FISH) result

Prognostic and predictive testing

Alternate test to confirm equivocal IHC result

Prognostic and predictive testing

Hereditary Genetic Testing

Recommended test to confirm hereditary breast and ovarian cancer (HBOC) syndrome

Includes only BRCA1/BRCA2 genes

Acceptable test to confirm HBOC syndrome

Includes only BRCA1/BRCA2 genes

Recommended test to confirm diagnosis of HBOC in individuals with a personal or family history of breast and/or ovarian cancer

Refer to the Hereditary Breast and Ovarian Cancer Test Fact Sheet for full list of genes tested

Recommended test to confirm diagnosis of hereditary cancer syndrome in individuals with a personal or family history consistent with features of more than one cancer syndrome

Refer to the Hereditary Cancer Panel Test Fact Sheet for full list of genes tested

Recommended test if there is a known familial sequence variant previously identified in a family member

Monitoring

Use to monitor therapy and identify disease recurrence in metastatic breast cancer

Medical Experts

Contributor
Contributor

McMillin

Gwendolyn A. McMillin, PhD
Professor of Clinical Pathology, University of Utah
Scientific Director, Mass Spectrometry Platform; Medical Director, Clinical Toxicology and Pharmacogenomics, ARUP Laboratories
Contributor

References

  1. PharmGKB

    Clinical Pharmacogenetics Implementation Consortium, Dutch Pharmacogenetics Working Group, Canadian Pharmacogenomics Network for Drug Safety. PharmGKB. Stanford, CA. [Accessed: Jun 2020]

    Online
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