March marks National Colorectal Cancer Awareness Month — a time to spotlight one of the most preventable cancers, yet one that continues to claim lives due to screening gaps and delayed detection. Over one-third of adults aged 45 and older in many developed countries remain unscreened, missing opportunities to catch precancerous changes before they become cancer.
What many people don’t realise is that colorectal cancer develops silently, often without symptoms, from precancerous polyps that take years to transform into cancer. This extended timeline is actually a gift: it creates a significant window for early detection and intervention.
Central to modern screening is a suite of biomarkers — measurable signals in blood and stool that reveal abnormal changes in the colon before symptoms develop. Understanding these biomarkers transforms screening from a vague recommendation into a tangible, informed health choice. This Awareness Month is an opportunity to learn how biomarker-informed screening works and why starting at age 45 matters more than ever.
Why Colorectal Cancer Screening Matters
How Cancer Develops From Polyps
Colorectal cancer rarely appears suddenly. Instead, it typically emerges through a well-documented progression: normal colon tissue → adenomatous polyps → precancerous changes → cancer. This sequence can unfold over 10 to 15 years or longer, providing a critical window for intervention.
Adenomatous polyps are growths in the colon lining that begin as benign but carry the potential to transform into cancer over time. Not all polyps become cancer — some remain dormant — but early removal of polyps virtually eliminates the risk they will progress to malignancy.
During this multi-year progression, cellular changes occur at the molecular level. Genes like APC and KRAS accumulate mutations, DNA methylation patterns shift, and precancerous cells begin shedding DNA into the bloodstream and stool. These molecular signals are what biomarkers detect, sometimes years before visible cancer develops.
Why Early Stages Often Have No Symptoms
This is the critical insight that transforms screening from optional to essential: early-stage colorectal cancer and precancerous polyps typically cause no symptoms at all. Many people feel completely healthy whilst harbouring significant precancerous changes.
By the time someone experiences symptoms — blood in stool, persistent changes in bowel habits, unexplained weight loss, or abdominal pain — cancer may have already progressed to a more advanced stage, making treatment more complex and outcomes less favourable.
This silent progression is precisely why screening is so powerful. Rather than waiting for symptoms to appear, screening detects changes whilst they remain early, highly treatable, and often curable.
Screening Starts Earlier Than Many People Think
Why Age 45 Matters
The recommended screening age in many developed countries recently shifted from 50 to 45 for average-risk adults. This change wasn’t arbitrary — it reflects emerging data on rising early-onset colorectal cancer in younger adults and the proven benefits of earlier detection.
Starting screening at 45 rather than 50 extends the detection window, catching more precancerous polyps before they advance and identifying any cancers whilst they remain in earlier stages. For individuals with family history of colorectal cancer, personal history of polyps, or inflammatory bowel disease, screening may begin even earlier.
Biomarker-based screening makes this earlier initiation more accessible, as many stool and blood-based tests can be done at home without the preparation and scheduling demands of colonoscopy.
Rising Early-Onset Colorectal Cancer
A concerning trend has emerged over the past two decades: colorectal cancer diagnoses in adults under 50 have steadily increased, whilst rates in older adults have declined due to improved screening. This paradox underscores the importance of earlier screening awareness, particularly for younger adults who may not yet view colorectal cancer as a personal health priority.
Reasons for rising early-onset cases remain incompletely understood but likely involve lifestyle factors, dietary patterns, obesity trends, and possibly environmental exposures. Regardless of cause, the trend reinforces that colorectal cancer is no longer a disease only of older adults — younger people need awareness and access to screening too.
Key Biomarkers Used in Colorectal Cancer Screening
Biomarkers in colorectal cancer screening fall into two categories: stool-based markers that detect abnormal cells or DNA in faeces, and blood-based markers that capture circulating signals of precancerous or cancerous changes.
FIT — Detecting Hidden Blood
The faecal immunochemical test (FIT) is one of the oldest and most widely validated screening biomarkers. FIT detects microscopic amounts of blood in stool that are invisible to the naked eye but may indicate precancerous polyps or cancer higher in the colon.
FIT is non-invasive, requires a simple at-home stool sample, and can be repeated annually or every one to two years as part of a screening regimen. A positive FIT result signals the need for colonoscopy to identify the source of bleeding and remove any polyps.
The strength of FIT is its simplicity and accessibility; its limitation is that it detects mainly bleeding lesions and may miss some polyps that don’t bleed. This is why FIT is often paired with other biomarkers or colonoscopy to provide comprehensive screening.
Stool DNA Tests and Methylation Markers (SEPT9/SDC2)
More recent stool-based screening tools analyse DNA shed from colon cells, looking for mutations and abnormal methylation patterns associated with precancerous changes and cancer. Two particularly important markers are SEPT9 and SDC2 methylation.
These methylation markers reflect epigenetic changes — chemical modifications to DNA that affect gene expression — and are associated with adenomatous polyps and colorectal cancer. Stool DNA tests can detect some polyps that FIT might miss, particularly larger precancerous lesions.
The advantage of stool DNA testing is that it captures molecular signals of dysplasia (abnormal cell growth) rather than only bleeding. However, stool DNA tests are typically performed less frequently than FIT — often every three years — and are more expensive. They are particularly valuable for individuals who want a single, comprehensive assessment or who prefer less frequent testing.
CEA and CA19-9
Carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA19-9) are blood-based tumour markers that can be elevated in colorectal cancer and other conditions. These markers are used more commonly for monitoring people who have been diagnosed with colorectal cancer rather than for initial screening.
After colorectal cancer diagnosis and treatment, serial CEA and CA19-9 measurements help oncologists track whether the cancer has recurred or spread. Rising levels may signal treatment failure or recurrence, prompting additional imaging or intervention. Stable or declining levels suggest effective treatment response.
These markers are less specific for early detection because they can be elevated in benign conditions and are typically not sensitive enough to reliably detect early-stage cancer in asymptomatic individuals.
ctDNA and Emerging Monitoring Tools
Circulating tumour DNA (ctDNA) represents fragments of cancer-derived DNA that appear in the bloodstream when cancer cells are present or actively dividing. ctDNA testing is an emerging approach to cancer monitoring and recurrence detection, offering potential advantages in sensitivity and specificity over older tumour markers.
For individuals with diagnosed colorectal cancer, ctDNA monitoring may become part of surveillance strategies to detect early recurrence. Liquid biopsy approaches — which analyse blood for cancer-specific signals — represent the future of non-invasive cancer monitoring, though their role in initial screening is still being established.
What Biomarkers Can Tell You
Screening vs. Diagnosis
A critical distinction: biomarker screening results indicate potential abnormality requiring clinical investigation, but biomarkers alone do not diagnose cancer or precancerous disease.
A positive FIT result, for example, indicates that microscopic blood has been detected in stool. This may be due to a polyp, bleeding haemorrhoids, inflammatory bowel disease, or rarely, cancer. The only way to determine the source is colonoscopy, which allows direct visualisation and biopsy if needed.
Similarly, a positive stool DNA test indicates that abnormal methylation patterns or mutations have been detected, suggesting possible precancerous changes. Again, colonoscopy is required to identify, visualise, and potentially remove any lesions.
The biomarker’s role is to identify who needs further investigation, not to definitively diagnose what is present. This is why biomarker screening is complementary to — not a replacement for — colonoscopy and clinical evaluation.
Monitoring After Diagnosis
Once colorectal cancer is diagnosed and treated, biomarkers guide monitoring for recurrence. CEA and CA19-9 levels are measured periodically; rising levels may indicate recurrence, whilst stable levels suggest controlled disease. ctDNA monitoring is emerging as a sensitive approach to detecting early recurrence before clinical symptoms appear.
At-Home Screening and Biomarker Awareness
Convenience and Access
One major advantage of biomarker-based screening is accessibility. Stool-based tests (FIT, stool DNA) and blood draws can be performed at home or in community settings without sedation, fasting, or the time commitment colonoscopy requires.
For individuals hesitant about colonoscopy, anxious about medical procedures, or with limited access to gastroenterology services, biomarker-based screening offers a practical entry point into the screening process. An at-home FIT or stool DNA test is far more likely to be completed than colonoscopy for someone avoiding medical facilities.
Moreover, because biomarker tests are non-invasive, they can be repeated more frequently than colonoscopy, offering ongoing monitoring between colonoscopy intervals or as standalone screening strategies in some clinical pathways.
When Clinical Follow-Up Is Needed
It’s crucial to understand that a positive biomarker screening test is not an endpoint — it’s a signal requiring clinical follow-up.
A positive FIT or stool DNA result warrants discussion with a healthcare provider and typically colonoscopy to investigate. A healthcare provider will assess the significance of the result, evaluate personal risk factors, and determine the appropriate next step. In some cases, additional imaging or specialist referral may be needed.
This is where the balance between convenience and clinical oversight becomes important. Biomarker screening makes screening more accessible and may encourage earlier participation, but results must always be interpreted by healthcare professionals in the context of your personal history and symptoms.
Awareness Month as a Reminder for Preventive Health
National Colorectal Cancer Awareness Month serves as an annual prompt to consider your screening status. Whether you’re approaching age 45, have never been screened, or haven’t had screening in several years, March is an opportunity to assess where you stand and take action.
Screening conversations don’t have to be intimidating. Many healthcare providers now discuss multiple screening options — colonoscopy, FIT, stool DNA testing, and others — allowing you to choose the approach that aligns with your preferences and comfort level.
The overarching message is simple: colorectal cancer is highly preventable when caught early through screening. Biomarkers have made screening more accessible, convenient, and personalised than ever before. Understanding how these biomarkers work empowers you to make informed screening decisions and take control of your colorectal health.
Final Thoughts: Control Through Knowledge
Colorectal cancer screening represents one of medicine’s great success stories — a disease with a clear prevention pathway and highly effective interventions when precancerous changes are identified. Yet success depends on screening participation.
Understanding colorectal cancer biomarkers transforms screening from a mysterious procedure into a comprehensible health strategy. This Awareness Month, consider your screening status. If you’re 45 or older and unscreened, discuss options with your healthcare provider. Screening dramatically increases the likelihood that precancerous changes will be caught early and removed before they progress to cancer.
Educational Disclaimer
This article is educational and does not constitute medical advice, diagnosis, or treatment. Biomarker screening results require clinical interpretation by a qualified healthcare provider. A positive screening biomarker does not diagnose cancer or precancerous disease; it indicates the need for further clinical evaluation. Normal biomarker results do not eliminate cancer risk. Screening decisions should be made in consultation with your healthcare provider, taking into account your age, risk factors, family history, and personal preferences. This content supports informed health conversations — it does not replace professional medical evaluation or clinical care.
