Screen for 50 cancers? The Galleri Cancer Screening test
Cancer is a disease that affects millions of individuals around the world annually. Traditional cancer detection procedures are time-consuming and often associated with an increase in personal and economic burden. The Galleri test is an alternative screening test with promising results.
Individuals eligible for the Galleri test include adults with an elevated risk for cancer, individuals aged 50 and older, and individuals experiencing cancer symptoms. This multi-cancer early detection (MCED) test relies on circulating tumour cell-free DNA (cfDNA) in the bloodstream to detect over 52 types of cancer. In most cancer types, the detectability increases with cancer stage as the proportion of cfDNA in the bloodstream also increases with the cancer stage.
Results from the test are received in 2 weeks following the blood draw and should be interpreted by your healthcare provider. Although the Galleri test has promising results, it brings with it a few limitations.
The Galleri test does not detect all cancers, the test does not measure your genetic risk of developing cancer in the future, the test has not been cleared by the FDA, and most importantly, it should be used in addition to other screening procedures.
This video is provided for general and educational information only. It is meant to guide individuals who fit the eligibility criteria towards discussing the test with their healthcare providers.
The Galleri test is a multi-cancer early detection (MCED) blood test that screens for a signal shared by more than 50 types of cancer. It is intended for adults at an elevated risk for cancer, such as those aged 50 or older, and works by analyzing DNA fragments shed by cancer cells into the bloodstream.
How the test works
Cancer cells shed cell-free DNA (cfDNA) fragments into the bloodstream, which differ from the DNA of healthy cells. The Galleri test looks for abnormal methylation patterns on these cfDNA fragments that could indicate the presence of cancer.
- Result interpretation: If a cancer signal is detected, the test can also predict the likely organ or tissue where the cancer originated. This helps guide a healthcare provider on the next steps for a diagnosis.
- A "point-in-time" test: The Galleri test identifies DNA from cancer cells present at the time of the blood draw. It is not a hereditary or genetic risk assessment for future cancer risk.
- Requires further testing: A positive Galleri test does not mean a person has cancer. A confirmed diagnosis requires additional diagnostic testing.
It is essential to understand the test's performance metrics, which show both strengths and weaknesses.
Strengths
- High specificity: The test has a high specificity rate (99.5% in some studies), which means a low false-positive rate (about 0.5%). This helps minimize unnecessary diagnostic procedures.
- Actionable results: If a cancer signal is found, the test can accurately predict the cancer's origin in most cases, aiding in the diagnostic workup.
- Complementary to existing screening: When used alongside recommended screenings, such as for breast, cervical, and colorectal cancers, it has been shown to increase the number of cancers detected.
Limitations
- Variable sensitivity: The test's sensitivity, or its ability to detect cancer, varies widely depending on the type and stage of cancer.
- Early vs. late stage: Sensitivity is significantly lower for early-stage cancers (e.g., about 16% for Stage I) and much higher for late-stage cancers (e.g., over 90% for Stage IV).
- Cancer type: The ability to detect specific cancer types can also differ.
- False negatives: Because overall sensitivity is not 100%, the test can miss some cancers, resulting in a false-negative result.
- Regulatory status and cost: The test is not yet FDA-approved and currently has an out-of-pocket cost of around $950, as it is not generally covered by insurance.
The Galleri test is designed to complement existing, guideline-recommended cancer screenings, not replace them. For adults considering the test, especially those 50 and over, it is essential to discuss the potential benefits and limitations with a healthcare provider. The test can increase the chances of early detection for certain cancers, but the risk of a false positive result triggering additional, potentially invasive procedures should be considered.
This is for informational purposes only. For medical advice or diagnosis, consult a professional.