Can Blood Tests Really Detect Cancer? What to Know About MCED and PRS Testing

About 39.9% of people in the U.S. will be diagnosed with cancer during their lifetime. Because many cancers do not cause symptoms right away, it is natural to wonder if early detection could improve outcomes.

As preventive and genetic testing continue to advance, so does interest in early cancer detection.

Two newer options generating attention are Multi-Cancer Early Detection (MCED) and Polygenic Risk Score (PRS) testing.

MCED uses a blood sample to look for possible cancer signals before symptoms appear, while PRS uses your genetic information to estimate your long-term risk for conditions like heart disease, diabetes, and some cancers.

While these tools show promise, they raise important questions about accuracy, cost, and follow-up testing.

As a board-certified family medicine physician at PartnerMD, I often help patients navigate the uncertainty that comes with emerging technology. The goal is not to promote testing, but to help you understand the benefits, limitations, and uncertainties involved.

Let's explore how MCED and PRS testing work, the options currently available, and whether these tools may fit in your preventive care plan.

Key Takeaways

• MCED testing looks for possible cancer signs in the blood before symptoms appear, but it does not diagnose cancer on its own.
• PRS testing estimates inherited risk for certain conditions by analyzing small genetic variations.
• Neither test replaces standard screenings like mammograms, colonoscopies, or routine preventive care.
• These tools may benefit those seeking a more personalized, data-driven approach to prevention, especially when guided by a physician.
• Most MCED and PRS tests are not yet FDA approved or covered by insurance.

While screening has improved over time, it still does not cover a broad range of conditions. We routinely screen for cancers like breast, colon, cervical, prostate, and lung, but the reality is that many cancers still do not have standard screening options.

At the same time, our understanding of genetics continues to evolve. Risk is rarely tied to a single gene. Instead, it is often the result of many small genetic variations.

This is where newer tools like MCED and PRS testing may provide additional insight.

What is Multi-Cancer Early Detection (MCED) Testing?

MCED testing is best thought of as an early signal, not the final answer.

These blood tests look for small fragments of genetic material that may be released into the bloodstream by cancer cells. In some cases, they can detect aggressive cancers that don't have screening options and may even suggest where cancer began in the body.

At PartnerMD, we offer Grail's Galleri test, which is an MCED test that screens for signals linked to more than 50 cancers using a blood sample.

While testing is still evolving, studies continue to show promising results. In the PATHFINDER 2 trial, about 6 in 10 people with a positive MCED result were later confirmed to have cancer after follow-up testing.

It is important to keep a few things in mind:

• A positive result does not confirm cancer.
• A negative result does not completely rule out cancer.
• Follow-up imaging or diagnostic testing is often required.
• MCED testing does not replace recommended screenings like mammograms or colonoscopies. 

What is Polygenic Risk Score (PRS) Testing?

Unlike MCED testing, PRS testing does not look for active disease. Instead, it estimates your inherited risk for developing certain conditions over time.

By analyzing thousands of small genetic variations across your DNA, PRS testing compares your risk to your general population for conditions such as heart disease, type 2 diabetes, high cholesterol, and some cancers, including prostate, breast, and colorectal.

At PartnerMD, we offer OpenDNA CardioRisk+, an AI-supported PRS test designed to access an individual's long-term risk for cardiovascular and cardiometabolic conditions.

Your genes are not your destiny.

Think of your DNA as a blueprint, not a verdict. Lifestyle factors like nutrition, exercise, sleep, stress management, and preventive care still play a major role in your long-term health outcomes.

PRS testing may be especially useful for people whose risk falls in the middle, where decisions about prevention, screening frequency, or lifestyle changes are not always clear.

What Are the Limitations of MCED and PRS Testing?

While MCED and PRS testing offer promising insights, they also have limitations. MCED tests can produce false positives or miss certain cancers, while PRS testing estimates risk rather than predicting whether disease will occur. Most tests are not FDA approved, and follow-up testing may be needed after abnormal results.

Because of this, these tools are often most useful when interpreted alongside your medical history, family history, and overall health goals.

While these tests are not for everyone, they could be a good fit for those who:

• Prefer a data-driven approach.
• Feel comfortable with some uncertainty.
• Are open to follow-up testing if needed.
• Want more personalized information to guide prevention decisions.

How Much Do MCED and PRS Tests Cost?

Cost is another factor to consider before pursuing these tests.

Most MCED tests are typically not covered by insurance. Depending on the company and type of test, out-of-pocket costs often range from $500 to $1,000 or more. 

PRS testing costs can also vary depending on whether the test evaluates one condition or multiple conditions, or includes physician interpretation and counseling. Some out-of-pocket costs for PRS tests can range from $200 to $400. 

Before moving forward, it is important to understand not only the upfront testing cost, but the potential need for additional follow-up appointments, imaging, or diagnostic testing.

The Bottom Line

MCED and PRS testing may offer helpful insights for some people, but they are not replacements for routine screenings or preventive care. Instead, they are tools that can add context when interpreted alongside your health and family history, and overall goals.

If you are considering either test, bring this topic up at your next appointment. Together with your PartnerMD physician, you can discuss your health goals, preventive care plan, and whether these tools make sense for you.

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