Why Biomarker Testing Should Happen Early for Every Patient With Colorectal Cancer

Biomarker testing is no longer optional in colorectal cancer care, according to Dr. John Marshall, chief medical officer and a member of the Board of Directors of the Colorectal Cancer Alliance, as well as a gastrointestinal medical oncologist at MedStar Georgetown University Hospital. As the understanding of colorectal cancer evolves, Marshall says physicians increasingly recognize that the disease is not one cancer but many distinct diseases driven by unique molecular alterations.

For decades, colorectal cancer was largely viewed as a single disease. Today, advances in molecular testing have revealed that colorectal cancer is actually a collection of biologically distinct diseases driven by different genetic alterations. Marshall says this growing understanding is transforming treatment selection and reinforcing the need for comprehensive biomarker testing as early as possible after diagnosis.

In an interview with CURE, Marshall discussed how biomarkers such as microsatellite instability (MSI), BRAF and RAS mutations are reshaping colorectal cancer care, why testing should occur early in the disease course and what patients should ask their care teams about their tumor's molecular profile.

What Is Biomarker Testing?

Biomarker testing analyzes a tumor for specific genetic or molecular characteristics that may influence how the cancer behaves or responds to treatment.

In colorectal cancer, several biomarkers are already used to guide treatment decisions, including microsatellite instability (MSI), BRAF mutations and RAS mutations. Researchers are also identifying additional biomarkers that may help further personalize care.

"We know that different genes are broken in different cancers," Marshall explained.

Rather than treating every colorectal cancer the same way, biomarker testing allows physicians to better understand the unique biology of an individual's tumor.

How Biomarkers Are Changing Treatment

Marshall compared traditional cancer treatment to breaking a light bulb.

Historically, many therapies were designed to broadly destroy cancer cells. While effective for some patients, these approaches often lacked precision.

"Most of the drugs we have just break the light bulb," Marshall said.

Biomarker-driven therapies, however, work differently. Instead of targeting the end result of cancer growth, they may target the specific genetic pathways driving the disease.

"Now with biomarkers, we actually have drugs that will go over there and turn the light switch off in a targeted, precise way," he said.

This targeted approach has helped expand treatment options for certain patients and continues to shape the future of colorectal cancer care.

Why Testing Should Not Be Delayed

Despite growing recognition of the value of biomarker testing, Marshall said many patients still do not receive comprehensive testing when they are first diagnosed.

In some cases, testing is postponed until later in the treatment process because physicians believe they do not immediately need the information.

Marshall believes that approach is becoming outdated.

"There are still lots of patients whose doctors are not doing the genetic testing on their tumors," he said.

Some clinicians may say they will order testing later if it becomes necessary, but Marshall emphasized that obtaining biomarker information upfront is increasingly important as treatment options become more personalized.

"The answer is increasingly, 'No, you need to do it right away,'" he said.

Should Biomarker Testing Be Done for All Stages of Colorectal Cancer?

Traditionally, biomarker testing has often been associated with advanced or metastatic disease. However, Marshall said the field is moving toward broader testing across all stages of colorectal cancer.

As researchers identify new biomarkers and develop additional targeted therapies, having molecular information available early can help inform treatment decisions throughout a patient's care journey.

"Frankly, you need to do it for all stages of cancer," Marshall said.

Early testing can also ensure that patients and their healthcare teams are prepared if treatment plans change or if new therapies become available.

Why Are Biomarker Testing Rates Still Lagging?

Although precision medicine continues to advance, Marshall said testing rates have not kept pace with scientific progress.

Some providers may still view biomarker testing as something that can wait until later in the treatment process. However, delaying testing can leave patients and care teams without critical information that may influence treatment decisions.

As more targeted therapies become available for biomarker-defined subsets of colorectal cancer, knowing a patient's tumor profile at diagnosis becomes increasingly important.

Marshall believes broader awareness among both physicians and patients will be essential to improving testing uptake.

What Patients Should Ask Their Care Team

Marshall encouraged patients to take an active role in understanding their diagnosis and treatment options.

For patients with colorectal cancer, one important question is whether biomarker testing has been performed and what the results show.

"If you don't know what your biomarkers are, you need to," Marshall said.

Patients should feel empowered to ask their healthcare team whether testing has been completed, what biomarkers were identified and how those results may affect treatment decisions.

As precision medicine continues to evolve, understanding a tumor's molecular profile is becoming an increasingly important part of colorectal cancer care. Knowing that information may help patients and physicians make more informed treatment decisions and identify opportunities for targeted therapies that would not otherwise be considered.

For more news on cancer updates, research and education, don’t forget to subscribe to CURE®’s newsletters here.