Breast Cancer Biomarkers

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) 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+/PR+/HER2- 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.  Oncotype DX, EndoPredict, Mammaprint, and Prosigna are four representative multigene tests that are commercially available; specifics about these tests are detailed in the following table.

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 (IHC4) scores 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. 

Familial Risk (Hereditary) Genetic Testing

BRCA1 and BRCA2 are the best characterized and most prevalent breast cancer susceptibility genes, but CDH1, PALB2, PTEN, and TP53 pathogenic variants are also associated with a high risk of breast cancer and should be assessed alongside BRCA1 and BRCA2.  Pathogenic variants in additional genes (eg, ATM, BARD1, CHEK2, NF1, RAD51C, RAD51D, and STK11) 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 pathogenic variants in the breast cancer susceptibility 1 and 2 (BRCA1/2) genes with an appropriate brief familial risk assessment tool. Individuals who screen positive should be offered genetic counseling, and if appropriate, BRCA1 and BRCA2 testing. Routine testing is not recommended in individuals whose personal or family history or ancestry is not associated with an increased risk. 

The NCCN guidelines  continue to expand the criteria for testing individuals with 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 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 a family history of cancer but have had limited previous testing (eg, single-gene testing and/or absent deletion/duplication analysis) and are interested in pursuing multigene testing.

Testing may be considered in individuals with breast cancer that is first diagnosed before age 60 who do not meet any additional criteria; unaffected individuals with Ashkenazi Jewish ancestry; and 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 variant based on previous probability models (eg, Tyrer-Cuzick, BRCAPRO, Penn II).

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

For more detailed information about the criteria for genetic testing of breast cancer susceptibility genes, refer to the 2022 NCCN guidelines. 

Other Testing

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

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 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, 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 be seen in the setting of responding disease.

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+ breast cancer, to the active metabolite endoxifen. The NCCN does not 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 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, and the ARUP Laboratories Test Directory for access to the complete menu of pharmacogenetic tests available at ARUP.