Breast Cancer Biomarkers

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Medical Experts

Contributor

Bernard

Philip S. Bernard, MD

Professor of Pathology (Clinical), University of Utah

Medical Director, Molecular Oncology, ARUP Laboratories

Contributor

Gulbahce

H. Evin Gulbahce, MD, MSCI

Professor of Pathology, University of Utah

Medical Director of Anatomic Pathology and Subspecialty Director of Breast Pathology, ARUP Laboratories

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McMillin

Gwendolyn A. McMillin, PhD, DABCC (CC,TC), FADLM

Professor of Pathology (Clinical), University of Utah

Scientific Director, Mass Spectrometry Platform; Medical Director, Clinical Toxicology, ARUP Laboratories

Contributor

Wiltse

Heidi Wiltse, MS, LCGC

Genetic Counselor, ARUP Laboratories

Primary carcinoma of the breast is the most common type of breast malignancy. Breast cancer is diagnosed by breast biopsy or excision and is 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. Patients with early-stage invasive breast cancer and known ER-positive/PR-positive/HER2-negative status may benefit from prognostic biomarker panels that can provide information to guide decisions about adjuvant systemic therapy. Individuals considered to be at increased risk for hereditary cancer may also undergo testing for pathogenic variants (mutations) that are commonly associated with breast cancer, including variants in the BRCA1 and BRCA2 genes.^,

Quick Answers for Clinicians

How is human epidermal growth factor receptor 2 (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) testing. Breast cancer tumors are considered HER2 positive 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.^,

What is the role of gene expression signature testing 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.

Are serum protein biomarkers (tumor markers) useful for screening or managing breast cancer?

Protein biomarkers are not currently recommended for breast cancer screening. Existing 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 to monitor 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 latest guidelines, 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 meta-analysis 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 or other formalized cancer risk assessment to determine appropriateness of genetic testing for themselves or other specified family members. Genetic testing should be considered when it would impact medical management.^, Genetic testing may involve single-gene testing for pathogenic variants 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, CDH1, CHEK2, PALB2, PTEN, STK11, and TP53 might be included in such a panel. For more information, refer to the Familial Risk (Hereditary) Genetic Testing section.

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 to monitor metastatic breast cancer along with a 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

The diagnosis of breast cancer 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 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 antiestrogen therapy. ER status is used to determine whether a patient should 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.^,

Other Biomarkers in Early-Stage Disease

The 2022 American Society of Clinical Oncology (ASCO) and the National Comprehensive Cancer Network (NCCN) recommendations address prognostic biomarker panels that may be useful in guiding decisions about adjuvant therapy for patients with early-stage invasive breast cancer and known ER-positive/PR-positive/HER2-negative status. The results of this testing may help a clinician determine if a patient would benefit from adjuvant therapy and may predict the likelihood of breast cancer recurrence. Refer to the NCCN for guidance on available multigene assays.

Certain other biomarkers may be useful in guiding decisions about adjuvant endocrine therapy and chemotherapy when multigene assays are not available. Ki67 expression may be used in conjunction with other factors to guide decisions concerning postmenopausal patients with early-stage breast cancer. Immunohistochemistry 4, an algorithm that combines ER, PR, HER2, and Ki67 results into a single score, may be useful in postmenopausal patients with node-negative cancer or with 1-3 positive nodes, as long as the score has been validated by the performing laboratory.

Other Biomarkers in Metastatic Disease

The 2022 ASCO recommendations also address certain biomarkers that may assist in therapeutic decision-making for individuals with metastatic breast cancer.

Biomarkers in Metastatic Breast Cancer
Biomarker	Relevant Clinical Situation
BRCA1 and BRCA2 (germline)	When the patient is HER2 negative, the patient is a candidate for PARP inhibitor therapy
dMMR/MSI-H	When the patient is a candidate for a treatment regimen that includes an ICI
NTRK fusions	When the patient is a candidate for a treatment regimen that includes a TRK inhibitor
PD-L1^a	When the cancer is locally recurrent unresectable or PR negative, ER negative, and HER2 negative When the patient is a candidate for a treatment regimen that includes an ICI
PIK3CA variants	When the patient is HER2 negative, the patient is a candidate for a treatment regimen that includes a PIK3CA inhibitor and hormonal therapy
TMB	When the patient is a candidate for treatment with an ICI
^aFor more information, refer to the ARUP Consult PD-L1 Testing topic. dMMR, deficient mismatch repair; ICI, immune checkpoint inhibitor; MSI-H, microinstability-high; PARP, poly adenosine diphosphate-ribose polymerase; PD-L1, programmed death-ligand 1; PIK3CA, phosphatidylinositol 3-kinase inhibitor; TMB, tumor mutational burden; TRK, tyrosine kinase Source: Henry, 2022

Familial Risk (Hereditary) Genetic Testing

BRCA1 and BRCA2 are the best characterized breast cancer susceptibility genes, and pathogenic variants in these genes are most common in hereditary breast cancer; however, additional genes have been implicated (such as CDH1, PALB2, PTEN, STK11, and TP53). Assessing for pathogenic variants in these additional genes may be important alongside BRCA1 and BRCA2 in individuals at increased risk. Though less common, pathogenic variants in additional genes (eg, ATM, BARD1, CHEK2, NF1, NBN, RAD51C, and RAD51D) have also been associated with an increased risk of 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 individuals who have a personal or family history of breast, ovarian, tubal, or peritoneal cancer, or who have an ancestry associated with harmful variants in the breast cancer susceptibility genes BRCA1 and/or BRCA2, with an appropriate brief familial risk assessment tool. Individuals who screen positive should be offered genetic counseling, and if appropriate, genetic testing for BRCA1/2. The USPSTF recommends against routine risk assessment, genetic counseling, or genetic testing for individuals whose personal or family history or ancestry is not associated with an increased risk for a deleterious BRCA1/2 gene variant(s).

The NCCN guidelines continue to expand the criteria for testing when there is a clinical suspicion of 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 unaffected individuals with Ashkenazi Jewish ancestry or 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 with a personal or family history of cancer who have had limited previous testing (eg, single-gene testing and/or no previous deletion/duplication analysis) and are interested in pursuing multigene testing.

Genetic testing may be considered in individuals with breast cancer who are first diagnosed before age 65 and do not meet any additional criteria. Genetic testing may also be considered in affected or unaffected individuals who otherwise do not meet any of the previously mentioned criteria but have a 2.5-5% probability of having a BRCA1/2 pathogenic/likely pathogenic variant based on previous probability models (eg, Tyrer-Cuzick, BRCAPRO, BOADICEA). (Different cutoffs may be appropriate for other risk models and if other genes are considered.)

For more detailed information about the criteria for genetic testing of breast cancer susceptibility genes, refer to the 2024 NCCN guidelines.

Other Testing

Liquid biopsy and circulating tumor DNA (ctDNA) analysis in breast cancer are emerging areas of research interest, and these methods can be used in the assessment for PIK3CA mutations in hormone receptor-positive/HER2-negative breast cancer. If the liquid biopsy is negative, the NCCN recommends tumor tissue testing for PIK3CA. This testing is not currently part of the standard of care recommended by ASCO.

Circulating tumor cell (CTC) counts are not recommended as standard of care by ASCO and the NCCN.^, A recent meta-analysis suggests that CTC testing has clinical validity as a prognostic marker and may provide useful information for 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) testing may be used to monitor metastatic disease in conjunction with diagnostic imaging, patient 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 occur when the disease is responding to treatment.

The most recent NCCN guidelines do not include recommendations regarding the 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-positive breast cancer, to the active metabolite endoxifen. The NCCN does not recommend CYP2D6 genotyping to determine the optimal adjuvant endocrine treatment 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 Pharmacogenetic Working Group. In addition to the gene-based dosing 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.