Key Points
- Colon cancer begins as benign polyps in the colon lining that can turn cancerous if left untreated, and it often produces no symptoms in its early stages.
- The FDA approved Guardant Health's Shield Blood Test in July 2024, adding a blood-based option to traditional stool tests and colonoscopy for colorectal cancer screening.
- Screening is recommended starting at age 45, and early detection significantly improves survival rates and treatment outcomes.
How Colon Cancer Is Detected and Treated
Colon cancer, also called colorectal cancer, begins in the lining of the colon and is classified into stages 0 through 4 based on how deeply it has penetrated and whether it has spread. Stage 0 involves abnormal cells confined to the inner lining; stage 4 means the cancer has reached distant organs such as the liver or lungs. The disease often produces no symptoms in its early stages, which is why routine screening is the primary way it is caught before it becomes advanced.
Symptoms, when they do appear, can include blood in the stool, rectal bleeding, a persistent feeling of incomplete bowel movements, fatigue, and unexplained weight loss. These signs can also stem from less serious conditions, so doctors generally advise seeing a physician if they last three weeks or more. Diagnosis typically starts with a medical and family history review, a physical exam, and then screening tests.
Screening options have expanded. Alongside colonoscopy and annual stool-based tests such as gFOBT and FIT, the FDA approved Guardant Health's Shield Blood Test in July 2024, giving patients a blood-based alternative. Treatment depends on stage and type: in stages 0, 1, and 2, surgeons can often remove cancerous polyps, and the smaller and more contained the polyp, the better the outlook. Risk factors include age, ethnicity, family history, inflammatory bowel disease, and Ashkenazi Jewish descent, while lifestyle factors such as diet, weight, and stress also play a role.
At a Glance
| Condition | Colon cancer (colorectal cancer) Cancer starting in the colon; staged 0 through 4 by how far it has spread. |
| Key Screening Test | Shield Blood Test by Guardant Health FDA-approved in July 2024 for colorectal cancer screening. |
| Regulator | U.S. Food and Drug Administration (FDA) Granted approval for the Shield blood-based screening test. |
| Screening Age | 45 years Recommended age to begin routine colon cancer screening. |
| Other Screening Methods | Colonoscopy, gFOBT, FIT, Second Generation FIT Stool-based tests recommended annually; colonoscopy visualizes the colon directly. |
| Key Term | Polyps Small benign growths in the colon lining that can become cancerous if untreated. |
| Key Term | 5-year life expectancy Compares survival of colon cancer patients five years after diagnosis to the general population. |
| Support Resource | Colorectal Cancer Alliance Helpline (877-422-2030) Free service connecting patients to resources and peer support. |
What the Shield Blood Test Means for Screening Rates
Why the Shield Blood Test Matters for Screening Rates
Colonoscopy remains the gold standard because it can both detect and remove polyps during the same procedure, but it requires bowel preparation, sedation, and time off work. Stool-based tests are non-invasive but must be repeated annually and are often skipped. The Shield Blood Test, approved by the FDA in July 2024, offers a middle path: a simple blood draw that could appeal to the millions of adults who avoid colonoscopy. For context, colorectal cancer screening rates in the U.S. have historically hovered around 60–70% of eligible adults, leaving a substantial gap that blood-based testing could help close.
Guardant Health's Commercial Opportunity
Guardant Health is primarily known for liquid biopsy tests in oncology, and the Shield approval extends its reach into the screening market. The company now competes with established stool-test makers and with colonoscopy providers. The commercial question is whether payers will cover the test at a price that makes it viable at scale, and whether primary care physicians will offer it routinely. If adoption is strong, Guardant gains a recurring revenue stream from a population that is screened every one to three years.
What This Means for Patients and Providers
For patients, the practical effect is more choice. Someone who has delayed screening because of colonoscopy logistics may now opt for a blood test, though a positive result still leads to a colonoscopy. For providers, the workflow changes: they must decide which test to offer first and how to follow up on abnormal results. The risk is that a less sensitive blood test could give false reassurance, so clear communication about follow-up is essential. The upside is that more people get screened at all, which is the goal.
What Patients and Providers Should Do Next
If you are 45 or older, the single most important step is to get screened — the method matters less than actually doing it.
- Ask your doctor about the Shield Blood Test if you have avoided colonoscopy; it was FDA-approved in July 2024 and may be covered by insurance.
- If you choose a stool-based test such as FIT or gFOBT, remember it must be repeated every year to be effective.
- See a doctor if you have blood in the stool, rectal bleeding, or a feeling of incomplete bowel movements lasting three weeks or more.
- Know your risk factors: age, family history, inflammatory bowel disease, and Ashkenazi Jewish descent all raise risk and may justify earlier or more frequent screening.
- If cost is a barrier, contact the Colorectal Cancer Alliance Helpline at 877-422-2030 for free resources and support.
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