Colorectal cancer is among the most common cancers in the United States and one of the very few that screening can prevent outright. Most cases begin as a benign polyp in the lining of the colon or rectum that grows slowly over years before becoming malignant, so finding and removing polyps stops cancer from ever developing. Diagnoses in adults under 50 have been rising steadily for decades, which is why the recommended starting age for screening moved down to 45.
Risk Factors
- Age: Risk rises with age, though the increase in younger adults means age alone no longer rules the diagnosis out.
- Personal or family history: Previous colon polyps or colorectal cancer, or a first-degree relative with either, raises risk and usually means starting screening earlier and repeating it more often.
- Inflammatory bowel disease: Long-standing ulcerative colitis or Crohn's disease involving the colon raises risk substantially, and calls for a separate surveillance schedule.
- Inherited syndromes: Lynch syndrome and familial adenomatous polyposis account for a minority of cases but carry very high risk, and they change screening for the whole family.
- Lifestyle: Processed and red meat, heavy alcohol use, smoking, inactivity, and obesity each contribute modestly. Type 2 diabetes is independently associated with higher risk.
Symptoms
Early colorectal cancer usually causes nothing at all, which is why screening exists. When symptoms occur they include rectal bleeding or blood mixed in the stool, a change in bowel habit lasting more than a few weeks, stools that become persistently narrow, cramping or abdominal pain, a feeling that the bowel does not empty completely, fatigue, and unintended weight loss. Iron deficiency anemia found on a blood test can be the first and only sign, and in an adult man or a postmenopausal woman it should prompt evaluation of the bowel rather than an iron prescription alone. Bleeding is commonly assumed to be hemorrhoids, and that assumption should only be made after the alternative has been excluded.
Screening and Prevention
The US Preventive Services Task Force recommends screening all adults at average risk from age 45 through 75, with the decision after 75 made individually. Several tests are acceptable. Colonoscopy examines the entire colon and removes polyps in the same session, and is repeated at long intervals when normal. Stool-based tests, including the annual fecal immunochemical test and the multi-target stool DNA test, are non-invasive but are repeated far more frequently and require a colonoscopy if positive. CT colonography is an option in some circumstances.
The important point is that an imperfect test completed on schedule prevents more cancer than a perfect test declined. Our guides to screening options beyond colonoscopy and to what your polyp results mean cover the choice and what follows it.
Diagnosis
A positive stool test, a suspicious finding on imaging, or symptoms lead to colonoscopy with biopsy, which establishes the diagnosis. From there, CT imaging of the chest, abdomen, and pelvis determines the extent of disease, and rectal tumors additionally require MRI to plan treatment. A blood test called CEA is often measured before treatment so it can be tracked afterward. Tumor tissue is tested for mismatch repair deficiency and related markers, because those results identify patients who respond particularly well to immunotherapy and can also signal Lynch syndrome, which has implications for relatives.
Treatment
Treatment depends heavily on location and extent, and is directed by a surgical and oncology team. Cancer confined to a polyp may be fully treated by removing it during colonoscopy. Most other localized colon cancers are treated surgically, with chemotherapy afterward when lymph nodes are involved. Rectal cancer is managed differently, frequently with chemotherapy and radiation before surgery. In advanced disease, chemotherapy combinations are standard, often including oral capecitabine, with targeted antibodies added according to tumor genetics. Tumors with mismatch repair deficiency may be treated with immunotherapy such as pembrolizumab, which in that specific group can work remarkably well.
What Primary Care Handles
Most of the work that reduces deaths from this cancer happens in a primary care office rather than an oncology one.
Getting the screening done
Ordering the test is the easy part; completing it is not. If a colonoscopy feels like an obstacle, say so, because a stool test you will actually do is a far better outcome than a colonoscopy you keep deferring. If a stool test comes back positive, the colonoscopy that follows is not optional, and arranging it promptly is the single most important step in the sequence.
Not explaining away red flags
Rectal bleeding in a younger adult, iron deficiency anemia in a man, or a bowel habit that has genuinely changed all warrant evaluation rather than reassurance, whatever your age. Our gastrointestinal care team arranges the workup and the referral.
Survivorship and family
After treatment, follow-up involves scheduled colonoscopy, imaging, and CEA monitoring for several years. A diagnosis also changes what relatives should do, often meaning earlier screening for siblings and children, and genetic counseling when an inherited syndrome is suspected.
When to Seek Care
Make an appointment for rectal bleeding or blood in the stool, a bowel habit that has changed for more than a few weeks, persistent abdominal cramping, unexplained weight loss, or a new diagnosis of iron deficiency anemia. The National Cancer Institute and the CDC publish clear overviews of screening and treatment.
If you are 45 or older and have never been screened, or you are putting off a test you have already been given, schedule a visit and let us find an option you will finish.