Underuse of Germline Genetic Testing in Cancer: A Missed Opportunity?
In this article
In patients diagnosed with cancer, germline (inherited) genetic testing is used to provide genetically targeted treatment and identify relatives who could benefit from personalized cancer screening and prevention. However, data are limited on how widely these tests are used and which patient groups are more likely to receive them. JAMA published an important study on June 5, 2023 that helps clarify testing patterns among 1.4 million patients diagnosed with cancer in California and Georgia, shedding light on the prevalence of germline genetic testing.
Note: Germline genetic testing and genomic testing are two different ways of obtaining genetic information. They serve different purposes and provide different types of information.
Germline Genetic Testing
Definition: Germline genetic tests examine an individual's inherited (germline) DNA. This DNA is present in the individual's egg or sperm cells and can be passed on to children.
Purpose: These tests identify inherited diseases or genetic predispositions. For example, mutations in BRCA1 and BRCA2 can increase the risk of breast and ovarian cancer.
Applications: They are used for risk assessment, genetic counseling and treatment planning in people with a family history of inherited disorders.
Genomic Testing
Definition: Genomic tests examine an organism's entire genome or a particular genetic region. They can analyze DNA in somatic (body) cells as well as germline DNA.
Purpose: Genomic tests are used to understand how genes function, how they interact, gene expression and how genes relate to diseases.
Applications: They are used in disease diagnosis, treatment selection, personalized medicine (targeted drugs), research and the broader understanding of genetic disorders.
Differences
- Focus: Germline testing focuses on inherited DNA, while genomic testing can examine the entire genome or specific genetic regions.
- Purpose: Germline tests generally identify inherited disease risk, whereas genomic tests aim to provide a broader genetic understanding.
- Scope: Germline tests usually focus on particular genes or mutations, while genomic tests may have a broader scope and examine the entire genome.
Both types provide genetic information, but they differ in the context in which they are used and the information they deliver. Test selection therefore depends on the need and the purpose of the research or treatment.
A Recent, Comprehensive Study of Germline Genetic Testing After Cancer Diagnosis
This study was conducted to determine how frequently germline genetic testing is performed in patients diagnosed with cancer.
Findings
- Among 1,369,602 patients diagnosed with cancer in California and Georgia, only 6.8% (93,052 people) underwent germline genetic testing.
- Testing rates were highest in patients with male breast cancer (50%) and ovarian cancer (38.6%).
- Testing rates were lower among non-White patients (Asian, Black and Hispanic).
- Between 67.5% and 94.9% of pathogenic results were identified in genes for which practice guidelines recommended testing.
Related topic: Inherited mutations cause 1 in 8 cancers: Should all patients be tested?
Conclusion and Commentary
This study provides important insight into how germline genetic testing is used among patients diagnosed with cancer.
Low uptake of germline genetic testing may represent missed opportunities to develop personalized treatment plans, such as those involving targeted drugs. It may also mean that family members miss opportunities for early screening and prevention strategies.
To increase the use of genetic testing in cancer care, it may help to:
- organize education and awareness campaigns,
- develop guidelines for healthcare professionals,
- reduce financial barriers, and
- make genetic counseling services more accessible.
Sources
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