Laboratory Tests for Breast Cancer Workup and Management
For initial breast cancer workup, obtain a minimum blood panel including complete blood count, liver function tests, renal function tests, alkaline phosphatase, and calcium levels 1. This basic laboratory assessment is standard across all newly diagnosed breast cancer patients and forms the foundation of your initial evaluation.
Initial Diagnostic Laboratory Workup
The essential laboratory tests fall into two categories: routine blood work and tumor biomarker assessment.
Basic Blood Work (Required for All Patients)
Obtain the following at initial diagnosis 1:
- Complete blood count (CBC)
- Liver function tests (AST, ALT, bilirubin)
- Renal function tests (creatinine, BUN)
- Alkaline phosphatase
- Calcium levels
These tests establish baseline organ function and help identify any metabolic abnormalities that might suggest metastatic disease, particularly bone or liver involvement.
Tumor Biomarker Testing (Mandatory)
Every breast cancer specimen must be tested for estrogen receptor (ER), progesterone receptor (PgR), HER2 status, and a proliferation marker such as Ki-67 2, 1. This is non-negotiable as these biomarkers directly determine treatment eligibility and prognosis.
ER and PgR Testing Specifications
- ER testing by immunohistochemistry (IHC) is the standard for predicting endocrine therapy benefit 3
- Report as ER-positive if ≥1% of tumor nuclei stain positive 3
- Tumors with 1-10% staining should be reported as "ER Low Positive" with a comment noting limited data on endocrine therapy benefit in this range 3
- ER-negative means <1% or 0% nuclear staining 3
- Similar principles apply to PgR testing, which serves primarily prognostic purposes in ER-positive disease 3
HER2 Testing Specifications
HER2 testing determines eligibility for multiple targeted therapies including trastuzumab, pertuzumab, and trastuzumab deruxtecan 4. The testing algorithm is critical:
- Use validated IHC or in situ hybridization (ISH) assays 5
- HER2-positive = IHC 3+ OR ISH amplified 5, 4
- HER2-equivocal = IHC 2+ → requires reflex ISH testing on same specimen 5
- HER2-negative = IHC 0 or 1+, or IHC 2+/ISH not amplified 4
Critical update: Pathology reports must now include a footnote distinguishing IHC 0 from IHC 1+ results, as IHC 1+ or 2+/ISH not-amplified tumors may be eligible for trastuzumab deruxtecan 4. This represents a significant shift in how we interpret "HER2-negative" disease.
Ki-67 and Proliferation Assessment
Include Ki-67 or another proliferation measure in the pathology report 2, 1. While methodological standardization remains imperfect, Ki-67 provides valuable prognostic information, particularly when values are clearly low or high 6.
Staging Laboratory Tests
Do NOT perform comprehensive metastatic workup (tumor markers, extensive imaging) in asymptomatic early-stage patients 2. This is a common pitfall—asymptomatic distant metastases are extremely rare in early breast cancer, and routine staging provides no benefit.
When to Pursue Additional Staging Labs
Order additional staging investigations (chest CT, abdominal imaging, bone scan) ONLY for 2, 1:
- Stage IIb or higher disease
- Clinically positive axillary nodes
- Large tumors (≥5 cm)
- Aggressive tumor biology
- Clinical signs, symptoms, or abnormal baseline labs suggesting metastases
Tumor markers (CA 15-3, CEA) should NOT be used for screening, diagnosis, or routine staging 2. Their role is limited to monitoring known metastatic disease.
Genomic Testing (Selective Use)
In HR-positive, HER2-negative early breast cancer with uncertainty about chemotherapy benefit, consider multigene expression assays 1. These include:
- Oncotype DX
- MammaPrint
- Prosigna (PAM50)
- EndoPredict
- Breast Cancer Index
Use these tests when clinical and pathological factors leave genuine uncertainty about chemotherapy benefit—not as routine screening 1, 6. They are most valuable in the "gray zone" of intermediate-risk disease (1-3 cm tumors, 0-3 positive nodes, intermediate Ki-67) 7.
Germline Genetic Testing
Offer BRCA1/2 germline testing and genetic counseling to patients meeting national criteria AND to those who are candidates for adjuvant olaparib therapy 1. This has both treatment implications (PARP inhibitor eligibility) and family screening implications.
Special Considerations and Pitfalls
Retesting Requirements
- Retest ER, PgR, and HER2 on recurrent or metastatic lesions when feasible 6
- If ER/PgR/HER2 are all negative on core biopsy, retest on surgical specimen to account for tumor heterogeneity 2
Quality Assurance
All laboratories performing biomarker testing must 6:
- Use analytically and clinically validated assays
- Participate in external quality assurance programs
- Maintain established acceptance/rejection criteria
- Undergo regular audits and accreditation
Emerging Markers (Not Yet Standard)
Do NOT use PD-L1 expression to guide treatment decisions in early breast cancer 1. While tumor-infiltrating lymphocytes (TILs) may provide prognostic information in triple-negative and HER2-positive disease, there are no established TIL thresholds for treatment decisions 1.
Follow-Up Laboratory Monitoring
During routine follow-up after curative treatment, do NOT perform routine tumor markers or comprehensive metabolic staging 2. Follow-up visits should focus on history, physical examination, and annual mammography. Laboratory tests are indicated only if symptoms or examination findings suggest recurrence.