CRC stands for colorectal cancer, a disease in which cells in the colon or rectum grow out of control. It is the third most common cancer diagnosed in the United States, with an estimated 154,270 new cases expected in 2025 and roughly 52,900 deaths. Despite those numbers, both incidence and death rates have been declining in recent years, largely thanks to wider screening and better treatments.
How Colorectal Cancer Develops
Most colorectal cancers don’t appear suddenly. They follow a slow, step-by-step process that typically begins with small, noncancerous growths called polyps on the inner lining of the colon or rectum. Over years, sometimes a decade or more, certain polyps accumulate genetic mutations that push normal cells toward cancer. Scientists call this progression the adenoma-carcinoma sequence.
The process usually starts with a mutation in a gene called APC, which acts as a brake on cell growth. When that brake fails, cells begin to multiply faster than they should. Additional mutations then pile on. A gene called KRAS, which tells cells when to grow, gets stuck in the “on” position in roughly 40 to 50% of colorectal cancers. Later mutations disable the body’s ability to repair DNA or trigger cell death, and eventually a benign polyp becomes an invasive cancer capable of spreading. This slow timeline is precisely why screening works so well: catching and removing polyps before they turn cancerous can prevent the disease entirely.
Symptoms to Watch For
Colorectal cancer often produces no symptoms in its early stages, which is one reason screening matters so much. When symptoms do appear, they depend on the tumor’s size and location in the large intestine. Common signs include:
- A persistent change in bowel habits, such as new diarrhea or constipation that doesn’t resolve
- Blood in the stool or rectal bleeding
- Ongoing belly discomfort, including cramps, gas, or pain
- A feeling that the bowel doesn’t empty completely
- Unexplained weight loss
- Unusual fatigue or weakness
None of these symptoms is unique to colorectal cancer. Many are caused by far less serious conditions like hemorrhoids or irritable bowel syndrome. But if any of them persist for more than a couple of weeks, they’re worth investigating.
Who Is at Risk
Risk factors for colorectal cancer fall into two broad categories: things you can’t change and things you can. On the non-modifiable side, family history is one of the strongest predictors. Having a first-degree relative (parent, sibling, or child) with CRC significantly raises your odds. Certain inherited genetic syndromes make the risk even higher. Lynch syndrome, caused by inherited defects in the body’s DNA-repair machinery, is the most common hereditary form. Familial adenomatous polyposis (FAP), which causes hundreds or thousands of polyps to develop in the colon during adolescence, carries a near-certain risk of cancer if the colon isn’t removed. A diagnosis before age 50 or a personal history of multiple cancers also raises suspicion for a genetic contribution.
On the modifiable side, smoking, heavy alcohol use, obesity, and a diet high in processed and red meat all increase risk. Physical inactivity is another well-established contributor. These lifestyle factors sometimes interact with genetic susceptibility, meaning a person with a modest inherited risk may tip the balance through unhealthy habits.
Rising Rates in Younger Adults
One of the most troubling trends in cancer medicine is the steady increase in colorectal cancer among people under 50. A few decades ago, a CRC diagnosis before 50 was unusual outside of people with known genetic syndromes. That’s no longer the case. Nearly 10% of new colorectal cancers worldwide now occur in people under 50, and early-onset rates have climbed in at least 27 countries. The average age at diagnosis in the U.S. has dropped from 72 to 67 in just over 15 years. Early-onset colorectal cancer is becoming a leading cause of cancer death among young adults in the United States.
Researchers are still working to understand why. Obesity, diet, antibiotic use, and changes in the gut microbiome are all under investigation, but no single explanation has emerged. This trend is a major reason the recommended age to start screening was lowered to 45.
Screening Guidelines
The American Cancer Society recommends that adults at average risk begin regular colorectal cancer screening at age 45. You have options: stool-based tests that look for blood or altered DNA, or structural exams like colonoscopy that let a doctor visually inspect the colon and remove polyps on the spot. The best test is the one you’ll actually do on schedule. If a stool-based test comes back positive, a follow-up colonoscopy is necessary to determine the cause.
People with a strong family history, a known genetic syndrome, or a personal history of inflammatory bowel disease typically need to start screening earlier and may need it more frequently. Your doctor can help determine the right timeline based on your individual risk.
Stages of Colorectal Cancer
Staging describes how far the cancer has spread and is the single biggest factor in determining treatment and prognosis. Doctors use the TNM system, which evaluates three things: the size and depth of the primary tumor (T), whether cancer has reached nearby lymph nodes (N), and whether it has spread to distant organs (M). These three factors combine into an overall stage from 0 to IV.
Stage 0 means abnormal cells are present only in the innermost lining of the colon. This is sometimes called carcinoma in situ and is not yet true cancer, though it can become cancer if untreated. Stages I through III represent progressively larger tumors or increasing spread to nearby tissues and lymph nodes. Stage IV means the cancer has metastasized to distant parts of the body, most commonly the liver or lungs.
Treatment by Stage
For early-stage colorectal cancer (stages I and II), surgery to remove the tumor and a margin of healthy tissue is often the only treatment needed. Many of these surgeries can be done with minimally invasive techniques, which means shorter hospital stays and faster recovery.
Stage III cancers, which have reached nearby lymph nodes, typically require surgery followed by chemotherapy to kill any remaining cancer cells. This combination significantly reduces the chance of recurrence. For rectal cancers, radiation is sometimes added before surgery to shrink the tumor and make it easier to remove.
Stage IV colorectal cancer is more complex. Treatment often involves chemotherapy combined with targeted therapies that block the blood supply to tumors or interfere with specific growth signals. Immunotherapy has emerged as a particularly effective option for a subset of patients whose tumors have a feature called high microsatellite instability (MSI-H), meaning their cancer cells have defective DNA repair. These patients, who historically responded poorly to conventional chemotherapy, often have strong and lasting responses to immunotherapy. In some cases, combining chemotherapy with immunotherapy before surgery can shrink locally advanced tumors enough to make them operable, with some patients achieving complete remission.
Survival Rates
Prognosis for colorectal cancer depends heavily on the stage at diagnosis. When the cancer is caught while still localized to the colon or rectum wall, the five-year survival rate is high. Regional disease, where cancer has spread to nearby lymph nodes, carries a lower but still meaningful chance of long-term survival. Distant metastatic disease has the lowest survival rate, though outcomes are improving with newer treatments. Overall, death rates from colorectal cancer have been falling by an average of 1.3% per year over the past decade, and new case rates have dropped by about 0.7% annually.
Reducing Your Risk
Beyond screening, several lifestyle choices can meaningfully lower your risk of developing colorectal cancer. Maintaining a healthy weight, staying physically active, limiting alcohol, and not smoking all matter. A diet rich in fruits, vegetables, and whole grains provides fiber and plant compounds that appear to protect the colon lining. These plant-based chemicals reduce inflammation in the gut through some of the same biological pathways targeted by aspirin.
Speaking of aspirin, data from eight randomized trials involving more than 25,000 patients found that daily aspirin use reduced deaths from several common cancers, including colon cancer. The benefit took about five years of consistent use to appear and lowered the 20-year risk of dying from colon cancer. Aspirin is not appropriate for everyone because of bleeding risks, so this is a decision to weigh with your doctor, especially if you have other risk factors for CRC. The combination of a plant-rich diet and aspirin is being studied as a low-cost prevention strategy, particularly for people at elevated risk.