Genetic testing for breast cancer offers a way to understand an individual’s inherited risk for the disease. This specialized testing identifies specific genetic changes that can increase the likelihood of developing breast cancer over a lifetime. Understanding the accuracy of these tests is important for individuals making informed health decisions.
Basics of Breast Cancer Genetic Testing
Genetic testing for breast cancer focuses on identifying inherited changes, known as mutations or pathogenic variants, in specific genes. Everyone inherits two copies of each gene, one from each parent. Genes like BRCA1 and BRCA2 are well-known examples, producing proteins that help repair damaged DNA and suppress tumor growth. When a harmful mutation occurs in one of these genes, it can disrupt this protective function, increasing cancer risk.
Beyond BRCA1 and BRCA2, other genes such as PALB2, ATM, CHEK2, CDH1, STK11, PTEN, and TP53 can also be associated with an increased risk of breast cancer. Genetic testing can involve panels that look for mutations in many of these genes simultaneously. This type of testing differs from tumor testing, which analyzes mutations within the cancer cells themselves to guide treatment, rather than inherited predisposition.
How Accuracy is Determined
The accuracy of genetic tests is typically described using scientific concepts like sensitivity and specificity. Sensitivity refers to a test’s ability to correctly identify individuals who truly have a specific genetic mutation. It measures how well the test detects true positives.
Specificity, conversely, indicates a test’s ability to correctly identify individuals who do not have the genetic mutation. This measures the rate of true negatives. For well-established genetic tests, particularly those for common BRCA1/2 mutations, both sensitivity and specificity are generally very high.
Factors Affecting Test Reliability
While genetic tests for established mutations are highly accurate, several factors can influence the overall reliability and interpretation of results. One common challenge arises with Variants of Uncertain Significance (VUS). A VUS is a genetic change whose effect on cancer risk is not yet clearly understood. Laboratories identify these changes, but they lack enough evidence to classify them as harmful or harmless.
VUS results are common, especially with multi-gene panel testing, and typically do not change immediate medical management. Over time, as more research is conducted and more data become available, many VUS are reclassified, often determined to be benign.
The quality of the laboratory performing the test also plays a role. Accredited laboratories must meet federal standards for quality and reliability, ensuring accurate analysis.
The current understanding of genetics also presents a limitation; not all genetic predispositions to breast cancer are currently known or included in testing panels. Therefore, a “negative” result does not eliminate all inherited risk, as there might be undiscovered genes or mutations not yet testable. Finally, genetic test results must always be interpreted alongside an individual’s personal and family medical history. This broader context helps provide a complete picture of an individual’s risk.
Understanding Your Test Results
Genetic test results can come in a few forms, each with distinct implications. A positive result indicates that a harmful genetic mutation linked to an increased risk of breast cancer has been identified. This signifies a predisposition, not a guarantee, that cancer will develop; many individuals with an identified mutation may never develop cancer.
A negative result means that no known harmful mutations were found in the genes tested. If a specific mutation was known in the family and the test confirms its absence, this is considered a “true negative,” meaning the individual’s risk is similar to the general population’s. However, if no specific family mutation was targeted, a negative result means no known mutations were found, but it does not eliminate all inherited risk, particularly from currently undiscovered genes or those not included in the panel.
For a Variant of Uncertain Significance (VUS) result, these are often considered benign, and medical management typically continues based on personal and family history. Regardless of the result, consulting with a qualified genetic counselor is important. Genetic counselors interpret findings within an individual’s unique health profile, guiding understanding of implications and next steps.