The words no one wants to hear are that “you may have cancer, and we need to do a physical biopsy on you.” Well, there may be other options to initially having a physical biopsy done.
And that option may be getting a liquid biopsy instead.
Liquid biopsies are a new and innovative way to detect cancer by analyzing blood samples for traces of tumor DNA or other cancer-related biomarkers.
Unlike traditional biopsies, which involve removing a tissue sample from the tumor, liquid biopsies offer a less invasive, quicker, and more convenient way to detect cancer, monitor disease progression, and even assess how a patient is responding to treatment.
There Are Different Kinds of Liquid Biopsies
Liquid biopsies are an emerging and non-invasive way to analyze cancer biomarkers in the blood, providing critical insights into the presence, type, and progression of cancer.
A number of different types of liquid biopsy tests are currently available with each having their own strengths and limitations. Below are the main types of liquid biopsies, along with their advantages and disadvantages.
1. Circulating Tumor DNA (ctDNA) Liquid Biopsy
What It Is:
ctDNA refers to fragments of DNA released from tumor cells into the bloodstream. This type of liquid biopsy looks for genetic mutations, alterations, or specific markers in ctDNA that are associated with cancer.
Pluses:
• Early Detection: Can detect genetic mutations and mutations related to cancer at very early stages, even before symptoms appear.
• Monitoring Disease Progression: ctDNA can be used to monitor how well a treatment is working or if the cancer is becoming resistant to therapy.
• Non-invasive: Unlike traditional biopsies, which require surgery or needle insertion, ctDNA liquid biopsies are non-invasive and much easier to administer.
Minuses:
• Sensitivity Issues: In some cases, ctDNA may be present in very low quantities, leading to the risk of false negatives. This can make detection harder in early-stage or localized cancers.
• Limited to Certain Cancers: While ctDNA testing is promising for certain cancer types (like lung, breast, and colon cancer), its sensitivity and utility can vary by cancer type, and it may not be effective in detecting all types of cancer.
2. Circulating Tumor Cells (CTCs) Liquid Biopsy
What It Is:
CTCs are actual cancer cells that have detached from a primary tumor and are circulating in the bloodstream. These cells can be isolated and analyzed to help us understand more about the cancer and its characteristics.
Pluses:
• Real-Time Monitoring: CTCs can be used to monitor real-time changes in cancer and its metastasis (spread), which can help determine the best course of treatment.
• Tracking Metastatic Disease: CTCs are especially useful in identifying metastatic disease, where the cancer has spread from its original site to other parts of the body.
• Direct Representation of Tumor Cells: CTCs are actual tumor cells, not just fragments of tumor DNA, so they may provide a more accurate representation of the cancer's genetic makeup and behavior.
Minuses:
• Detection Challenges: CTCs are typically present in very low quantities in the blood, which can make them difficult to detect, especially in early-stage cancers.
• Technological Limitations: The techniques used to isolate and identify CTCs are still evolving, and not all laboratories may have the necessary technology to perform these tests accurately.
3. Exosome-Based Liquid Biopsy
What It Is:
Exosomes are small vesicles (sacs) released from cells, including cancer cells, which contain RNA, proteins, and DNA. These exosomes can be isolated from a blood sample and analyzed for cancer-related information.
Pluses:
• Comprehensive Information: Exosomes contain a variety of biomolecules (RNA, DNA, proteins) that can provide a more complete picture of the cancer and its environment.
• Less Invasive: Like other liquid biopsy methods, exosome testing is non-invasive and can be easily repeated to monitor disease progression over time.
• Potential for Broader Use: Exosome-based liquid biopsies could be applied across a wider range of cancers due to the variety of biomarkers they carry.
Minuses:
• Technological Complexity: The analysis of exosomes requires sophisticated technology and expertise and is still under development.
• Sensitivity and Specificity: Although exosome tests show promise, sensitivity and specificity can still be an issue, leading to potential false positives or false negatives.
4. Circulating MicroRNAs (miRNAs) Liquid Biopsy
What It Is:
MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression and can be released into the bloodstream by tumors. The analysis of specific miRNAs in blood can provide valuable diagnostic and prognostic information about various cancers.
Pluses:
• Early Diagnosis: miRNA-based liquid biopsies can detect the presence of cancer at an early stage by identifying specific miRNAs linked to the disease.
• Less Invasive: Like other liquid biopsies, miRNA tests are non-invasive, with blood being the only sample needed.
• Ability to Detect Multiple Cancer Types: miRNAs have been implicated in many different types of cancer, so this test could potentially be used as a pan-cancer biomarker.
Minuses:
• Sensitivity Issues: miRNA testing may not be as sensitive in detecting early or low-burden cancers, especially when compared to ctDNA or CTCs.
• Complex Interpretation: miRNA expression can be influenced by other factors, such as inflammation, making it difficult to pinpoint cancer-related changes with high accuracy.
• Limited Clinical Validation: Although promising, miRNA-based liquid biopsies are still under research and are not yet fully validated for widespread clinical use.
5. Protein-Based Liquid Biopsy
What It Is:
Protein-based liquid biopsies focus on detecting tumor-associated proteins or protein biomarkers in the blood, such as CA-125 for ovarian cancer or PSA for prostate cancer.
Pluses:
• Widely Used: Certain protein markers, like PSA (prostate-specific antigen) and
CA-125, have been in clinical use for years and are well-understood by the medical community.
• Non-invasive: Like all liquid biopsy methods, protein-based tests are non-invasive and can be performed easily with a simple blood draw.
• Familiar and Reliable: Since some protein markers have been in use for a long time, healthcare providers are familiar with how to interpret the results, making them more easily integrated into clinical practice.
Minuses:
• Limited to Specific Cancers: Protein biomarkers tend to be specific to certain cancer types, which limits their utility for detecting a wide range of cancers.
• False Positives: Protein levels can be influenced by factors other than cancer, leading to potential false positives. For instance, PSA can be elevated due to benign prostate conditions.
• Lower Sensitivity: Protein markers are not always sensitive enough to detect early-stage cancers, and some cancers may not produce detectable proteins.
Cost of Liquid Biopsies for Cancer
The cost of a liquid biopsy can be significant, ranging from $500 to $3,000 or more, depending on the test’s complexity. While Medicare may cover liquid biopsies under certain conditions, particularly for patients with advanced cancer or those in clinical trials, it is not guaranteed.
Coverage often depends on the test being deemed medically necessary. Patients should work closely with their healthcare provider and Medicare to understand the specifics of their coverage and out-of-pocket costs for these tests.
For other insurance programs, you’ll need to check with your insurance provider to get clarity about what is and isn't covered.
(Reported Bottom Line Health, March 2025)
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