Clinical Laboratories Key to Breast Cancer Diagnosis and Treatment

In the United States, a woman’s average risk of developing breast cancer at some time during her life is about 13%, meaning women face a one in eight chance of developing the disease.[1] October, National Breast Cancer Awareness Month, highlights the burden of this disease to increase patient knowledge and to highlight the critical importance of regular screenings to improve survival rates.

Clinical laboratories play a vital role in all aspects of breast cancer care, including identifying the disease, describing, and understanding its traits, and providing critical information that can guide decisions on individualized treatment.

While breast cancer accounts for 30% of all new female cancers each year,[2] men are affected, too, though at a much lower rate of about one in every 833 men.

The causes of breast cancer are complex, with some types related to hereditary genetics and others linked to gene changes in cancer cells. The most well-known genetic determinants are inherited mutations in the BRCA 1 and BRCA 2 genes (BReast CAncer genes 1 and 2), which can be passed from either parent to child. When present, these mutations significantly increase the risk of breast cancer in women. For instance, among women who inherit a harmful BRCA 1 variant, 55% to 72% will develop breast cancer by age 70-80 years. Of those with the harmful BRCA 2 variant, 45% to 69% will develop breast cancer by that age.[3]

However, the risk for any one woman may involve many factors. Clinical laboratories conduct multi-gene biomarker testing, which helps identify patients at risk and those who are likely to benefit from a given therapy.

Genetic testing performed by clinical laboratories helps recognize whether someone has an inherited gene that could increase the chance of developing breast cancer. Those who have received a diagnosis of breast cancer are offered clinical laboratory tests to identify and characterize cancerous cells through the examination of biopsy samples. These tests reveal the type of breast cancer, the stage or extent of the cancer, and help guide a patient’s treatment plan.

Clinical laboratories also analyze the size of a tumor, determine whether there is possible lymph node involvement, and describe microscopic characteristics of tumors. This information helps to predict the likelihood of cancer recurrence and helps patients and oncologists to design long-term treatment strategies, which may include breast surgery, chemotherapy, hormone therapy, radiation, or other options.

Once surgery or other treatments have been completed, clinical laboratory tests can, by examining surgical margins and lymph nodes, detect any remaining cancer cells, which can suggest the need for further treatment. Biomarker testing on cancer tissue or fluid helps determine the most effective treatment options in individual cases.

Clinical laboratories also can perform advanced genomic and molecular testing to help pinpoint changes in DNA that may spur the growth of an individual’s tumor. This information can help oncologists make decisions regarding targeted drug therapies or immunotherapy drugs for treatment.

Adjuvant chemotherapy after breast surgery has been shown to reduce the recurrence of cancer, leading a National Institutes of Health panel to recommend it in most patients, but in some cases, it may be unnecessary. Gene assay tests can help predict the possible benefits of chemotherapy treatment, identifying patients with early breast cancer who may be spared adjuvant chemotherapy.[4] Gene expression tests provide more information about the cancer cells and help tailor personalized treatment, predicting which patients are most likely to benefit from chemotherapy to reduce the risk of recurrence of cancer after breast surgery.

Other clinical laboratory tests, such as a complete blood count (CBC), blood chemistry tests, and tumor markers, can help determine if a patient is well enough to undergo surgery, chemotherapy, or immunotherapy as part of treatment.

Breast cancer is the most common cancer in women, with more than 2 million cases diagnosed worldwide in 2018,[5] and nearly 300,000 new cases expected in the U.S. this year.[6] But over the years, the prognosis for long-term survival has improved dramatically. Currently, five-year survival rates for women with non-metastatic breast cancer are 91%, and the 10-year survival rate is 85%.[7]

This hopeful trend is attributed in large part to widespread use of screening programs that lead to early diagnosis, when treatment is most effective, and to advances in molecular understanding of tumors, and subtype classification that leads to treatment personalization.[8] Clinical laboratories play an essential role in this progress, resulting in better outcomes for all people with breast cancer.

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[1] American Cancer Society,,will%20never%20have%20the%20disease.

[2] American Cancer Society,,will%20never%20have%20the%20disease.

[3] National Cancer Institute,

[4] The New England Journal of Medicine,

[5] National Institutes of Health (NIH),

[6] American Cancer Society,,will%20never%20have%20the%20disease.

[7] American Society of Clinical Oncology (ASCO),,vary%20based%20on%20several%20factors.

[8] National Institutes of Health (NIH),

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