By Rodney Herbert

What Are Gene Expression Tests?

Gene expression tests are special lab tests that examine the activity of certain genes in a cancer tissue sample. Genes are like instruction manuals inside your cells. Not all genes are active (or “expressed”) at the same time. In cancer, some genes can be very active and drive the cancer to grow or spread. A gene expression test measures which genes in the prostate tumor are turned on and off. By doing this, the test creates a profile or “signature” of the tumor’s behavior urologytimes.com. In simple terms, it’s as if the test is “reading the cancer’s notes” to see how aggressive it might be.

These tests are done on tissue from your prostate tumor that was removed during a biopsy or surgery. You do notneed another procedure to get a gene expression test – the lab can use the existing biopsy tissue you already had taken​ urology.ucsf.edu. Even a small amount of cancer from the biopsy (as little as a 1mm piece) can be enough for testing​. The laboratory examines the tumor’s RNA (a chemical message from genes) to see the levels of specific genes. The result is usually given as a score or risk category that indicates how aggressive or risk-prone your cancer is.

Why Use Gene Expression Tests? (Checking Cancer Aggressiveness)

Doctors traditionally predict prostate cancer aggressiveness using factors like PSA level, Gleason score (how cancer cells look under a microscope), and tumor stage. While these are useful, they are not perfect. Sometimes, they overestimate the danger (leading to overtreatment), and other times they underestimate it​. Gene expression tests add another layer of information by looking at the tumor’s biology directly.

Think of it like this: If PSA and Gleason score are the “outside view” of the cancer, gene expression is the “inside view.” By analyzing the genes, these tests can give more precise insights into how likely the cancer is to grow quickly or spread​. For example, certain patterns of gene activity might suggest that the tumor is very active and likely to be aggressive, while other patterns suggest a quieter, slow-growing tumor.

In practical terms, a gene expression test can help classify a prostate cancer as low risk, intermediate risk, or high risk in terms of aggressiveness. This is sometimes called a genomic risk score or genomic classifier result. It doesn’t diagnose cancer (you already know you have cancer), but it predicts what might happen – such as the risk of the cancer spreading (metastasizing) or causing harm in the future​ ncbi.nlm.nih.gov.

For example, a low genomic risk score means the genes in the tumor look more like those in slow-growing cancers. A high score means the genes look more like those in aggressive cancers. Studies have found that these genomic scores can sometimes predict outcomes (like chance of metastasis) better than traditional measures alone​. In short, gene expression tests help doctors and patients get a clearer picture of how “nasty” or not the cancer might be.

How Gene Tests Guide Treatment Decisions

Because gene expression tests give insight into how aggressive the cancer is, they can help guide treatment decisions in prostate cancer. One of the biggest questions for many men with prostate cancer is whether they need treatment right away or if they can safely watch and wait (a strategy called active surveillance) for a while. Here’s how the tests can help:

  • Active Surveillance vs. Active Treatment: If a man’s cancer appears low-risk (for example, low PSA, low Gleason score), doctors might suggest active surveillance (regular monitoring with PSA tests, repeat biopsies, etc.) instead of immediate treatment. However, there’s always a worry: Could there be hidden aggressive disease that we’re missing? Gene expression tests like Oncotype DX or Prolaris can provide an extra check. If the gene test also comes back low-risk, it gives more confidence that surveillance is safe​. On the other hand, if the gene test shows the tumor has an aggressive genetic profile, the patient and doctor might decide to move to treatment (such as surgery or radiation) sooner rather than later​.

  • Choosing Treatment Intensity: For those who do need treatment, the test results might influence how aggressive the treatment should be. For example, a man with intermediate-risk cancer might be deciding between just surgery alone or surgery plus additional therapy (like radiation or hormone therapy). A high-risk genomic test result could tilt the decision towards adding more treatment, while a low-risk result might support a less aggressive approach. In fact, tests like Decipher are used after surgery to decide if additional treatments (like radiation or hormone therapy) are needed or not​. The idea is to personalize the treatment – treat intensively when genomics say the cancer is high-risk, and avoid unnecessary treatments when genomics say it’s low-risk​.

  • Peace of Mind or a Second Opinion from the Tumor: Many patients find that a genomic test result can either reassure them or push them to act. For instance, if everything else looks low-risk but you feel uneasy about “just watching” the cancer, a low-risk gene test result can give peace of mind that active surveillance is reasonable. Conversely, if you’re leaning toward avoiding treatment but the gene test comes back high-risk, it’s a strong sign to reconsider and possibly treat. It’s like getting a second opinion – not from another doctor, but from the tumor’s own genetics.

It’s important to note that gene expression tests don’t give a 100% certain answer (no test can predict the future with certainty). They provide probabilities and risk estimates. Doctors will always interpret the results alongside other factors like PSA, Gleason score, MRI findings, and your overall health​. The genomic test is one piece of the puzzle – an important piece that can tip the balance in decision-making, but not the only piece.

  • These tests have become more common, but not everyone gets one. When they first came out, hardly anyone was using them. Even now, only a small percentage of prostate cancer patients receive a gene expression test. One analysis from 2011–2021 found that less than 2% of eligible patients had one of these tissue tests done​ pmc.ncbi.nlm.nih.gov

    However, the use is growing each year​. More doctors are ordering them as more evidence comes out and as the tests become part of the conversation.

  • Doctors use them selectively. In my experience, doctors tend to suggest these tests for patients who are on the fence about treatment, especially younger patients with a long life expectancy. If a man is older or has other serious health issues, a genomic test might not change the plan (because those men might choose to treat or not treat based on age/health regardless of genomics). Indeed, research shows that younger patients are more likely to get genomic testing than older patients​, likely because younger men have more to gain from fine-tuning their treatment decisions. If you’re, say, 55 and otherwise healthy with a low-risk prostate cancer, a gene test might help decide if you can safely avoid treatment for now – that decision has big implications for potentially 20-30 years of your life. If you’re 80, the decision might be clearer from other factors alone.

  • Insurance and cost can be an issue. Patients often ask me if their insurance will cover these tests. Coverage varies – some insurance plans do cover them especially if the doctor provides a reason, but others might not. The tests can be expensive (several thousand dollars) if paid out-of-pocket. Always check with your insurance and ask if there are financial assistance programs. I’ve seen patients successfully appeal to get a test covered when it was really needed. The companies that make the tests sometimes have assistance programs as well.

  • The waiting and uncertainty. It usually takes a couple of weeks to get the results of a gene expression test. That waiting period can be anxiety-provoking. However, many patients feel it’s worth it because the result can provide clarity. When the result comes, make sure your doctor explains it in plain language. I often tell men, “Don’t get lost in the numbers; focus on what the numbers mean for you.” For example, whether your risk of progression is 5% or 50% is more important than the technical details of the score.

  • These tests don’t give a yes-or-no answer. A common misconception is that a genomic test will say “Yes, you must treat” or “No, you’re fine to wait.” In reality, it gives a risk estimate. It might say, for instance, “You have a 10% chance of metastasis in 5 years without treatment.” Some patients expect a black-and-white answer and can be a bit disappointed that it’s still a probability. It’s important to use that probability in decision-making. For example, some men are comfortable with a 10% risk and choose to watch the cancer, while others would feel uncomfortable unless the risk was below, say, 2%. It’s a personal value judgment informed by the test.

  • Discuss with your doctor how the result will be used before doing the test. In my advocacy, I emphasize informed decision-making. If your doctor suggests a Prolaris, Oncotype, or Decipher test, ask: “How will the results affect the next steps?” If the answer is, “If it’s low risk we will continue surveillance, if high we will treat,” then you know the test has a purpose. If even a low-risk result wouldn’t change your mind about treatment (or a high-risk result wouldn’t either), then think about whether you need the test. In other words, don’t do it just because it’s available – do it because the information will help you decide something.

  • From fear to empowerment. I’ve seen men go from fearful to confident after getting their genomic test results. One patient with a small low-grade tumor was very afraid of delaying treatment. He got an Oncotype DX test which showed a very low GPS score. This gave him the confidence to choose active surveillance, and years later he is still doing well without treatment. Another patient had what looked like intermediate cancer; his Decipher score came back high, and he decided to get combination therapy (surgery plus radiation). He felt justified in being aggressive and ultimately did well. In both cases, the test helped them feel more secure in their choice.

  • They are not magic crystal balls. I always remind patients: these tests improve the odds of getting the decision right, but they don’t guarantee it. A low-risk result doesn’t mean your cancer could never act aggressive, it means it’s unlikely to. There’s always a small chance of surprise. Likewise, a high-risk result isn’t a death sentence; it means be proactive because the risk is higher. Think of the test as a more informed “weather forecast” for your cancer​. It can tell you if there’s a storm likely, but not with absolute certainty. You still prepare based on the forecast, because it’s the best information you have.

  • Keeping perspective. Genomic testing is an evolving field.  The medical community goes from skepticism to a growing acceptance of these tools. Clinical trials are ongoing to measure how much these tests improve patient outcomes. Some doctors are big believers in them; others are more cautious, waiting for more proof. Don’t be surprised if you encounter mixed opinions. In the end, it’s one more piece of data. Use it to have a thoughtful discussion with your care team. Most importantly, feel comfortable with your treatment plan – these tests are there to help you feel more informed about your choice.