Standard, everyday blood tests, such as a Complete Blood Count (CBC) or a Comprehensive Metabolic Panel (CMP), are not screening tools for breast cancer, as they measure general health indicators, not tumors or cancer cells. However, specific types of blood tests are integrated into the management, monitoring, and risk assessment of the disease after a diagnosis has been established.
Standard Blood Work and Diagnosis
Routine blood work provides a baseline assessment of general physiological health. A Complete Blood Count (CBC) measures red blood cells, white blood cells, and platelets, helping identify conditions like anemia or infection. Anemia, characterized by low red blood cell counts, may sometimes be an indirect consequence of cancer or indicate spread to the bone marrow. The Comprehensive Metabolic Panel (CMP) checks electrolytes and the function of organs like the liver and kidneys. These tests ensure a patient is healthy enough for treatment and watch for complications arising from the cancer or its therapies.
Tumor Markers for Monitoring Treatment
Once a breast cancer diagnosis is confirmed, specialized blood tests for tumor markers become an important tool. These markers are substances, often proteins, produced by the cancer cells or by the body in response to the cancer. The most commonly used markers are Cancer Antigen 15-3 (CA 15-3) and CA 27-29, which measure the MUC1 protein shed into the bloodstream by tumor cells.
The primary role of CA 15-3 and CA 27-29 is to monitor the effectiveness of treatment and to detect a recurrence, particularly in patients with metastatic disease. A decrease in marker levels often suggests that the cancer is responding to therapy, whereas a sustained increase may indicate disease progression or relapse.
These markers are not reliable for mass screening because they lack sufficient sensitivity and specificity. For instance, up to 80% of patients with metastatic breast cancer may show elevated CA 15-3 levels, but only about 50% of those with early-stage disease will have an elevated result.
The Food and Drug Administration (FDA) has approved CA 15-3 and CA 27-29 specifically for monitoring purposes, and results are always interpreted in conjunction with physical exams and imaging scans. In some cases, an increase in these markers can signal a relapse an average of three months before it is clinically detectable by conventional imaging.
Genetic Testing for Inherited Risk
Genetic testing uses blood samples to assess a person’s inherited risk of developing breast cancer. This testing looks for germline mutations, which are alterations present in every cell that can be passed down through families. The most well-known genes screened are BRCA1 and BRCA2, but testing often includes others such as PALB2, ATM, and CHEK2.
The test determines if an individual has inherited a genetic variant that significantly increases their lifetime risk. For instance, women with an inherited BRCA2 mutation have a risk of developing breast cancer that can range between 61% and 77% over their lifetime. This testing identifies a predisposition rather than active disease.
Testing is typically recommended for individuals with a strong personal or family history, such as those diagnosed with breast cancer at a young age or those with triple-negative breast cancer before age 60. The results inform risk management strategies, which might include earlier screening, preventive medications, or prophylactic surgery.
The Future of Blood Testing for Breast Cancer
The most promising development in blood testing for breast cancer is the emergence of “liquid biopsies.” These advanced tests analyze a blood sample for tiny fragments of material shed by tumors, known as circulating tumor DNA (ctDNA). Detecting ctDNA offers a non-invasive way to gain information about the cancer’s genetic makeup and behavior.
Liquid biopsies hold potential for non-invasive early detection and more precise treatment matching. The technology is highly sensitive, allowing researchers to detect minimal residual disease (MRD)—microscopic cancer cells remaining after treatment—which can predict recurrence years before it appears on a scan. While revolutionizing cancer research, liquid biopsies are not yet standard for mass screening. Current efforts focus on validating ctDNA’s role in monitoring therapeutic response and predicting relapse risk.