Colorectal Cancer

If you’ve had an abnormal colorectal screening result, a concerning colonoscopy finding, new digestive symptoms, or have been told you might have colorectal cancer, Siteman Cancer Center offers a clear next step – with expert diagnosis, personalized treatment planning, and access to nationally recognized care tailored to your cancer and your life. 

The right diagnosis is where exceptional colorectal cancer care begins. At Siteman Cancer Center, specialists use advanced imaging, precision pathology, genomic testing, and multidisciplinary expertise to define colorectal cancer with clarity from the start – because getting the diagnosis right the first time can shape treatment options, speed access to care, and improve outcomes.  

The colorectal program at Siteman Cancer Center combines leading surgical expertise, advanced rectal cancer treatment approaches, dedicated young-onset colorectal cancer leadership, and a deep portfolio of clinical trials designed to bring the next generation of cancer care to patients today.  

Learn more about colorectal cancer symptoms, screening findings, diagnosis, and the treatment options available at Siteman below. 

What Is Colorectal Cancer?

Colorectal cancer begins in the lining of the colon, rectum, or anus. It is the third most common cancer in the United States, with more than 140,000 people diagnosed each year (PDF).. When found early, it is also one of the most treatable. 

Most colorectal cancers begin as small growths called polyps on the inner lining of the colon or rectum. Over time, certain types of polyps can become cancerous. This gradual progression is exactly why screenings are effective at preventing cancer. Screenings give physicians the opportunity to find and remove polyps before they become cancerous.

Colon cancer and rectal cancer are closely related. For both, the same type of cells become cancerous. Even though it’s the same kind of cancer cells because the rectum sits deep in the pelvis, rectal cancer often requires a different treatment approach than colon cancer. At Siteman, our multidisciplinary team of WashU Medicine specialists excels in both. 

What Causes Colorectal Cancer? 

The exact cause of colorectal cancer is not fully understood, but a combination of lifestyle, environmental, and genetic factors can increase a person’s risk. 

Risk factors are not the same as a direct cause. Many people with risk factors never develop colorectal cancer, and some people without known risk factors do. But understanding your risk is an important step toward prevention and early detection through routine screenings. 

Common risk factors for colorectal cancer include:
 

• Age: 45 or older, though colorectal cancer is rapidly rising among younger adults  
• A personal or family history of colorectal cancer or polyps 
• Inherited genetic syndromes, including Lynch syndrome (HNPCC) and familial adenomatous polyposis (FAP) 
• Inflammatory bowel diseases such as Crohn’s disease or ulcerative colitis 
• A diet high in processed or red meat and low in fiber 
• Physical inactivity, obesity, or type 2 diabetes 
• Behaviors like tobacco use and heavy alcohol consumption 

WashU Medicine physicians and genetic counselors at Siteman are experienced in identifying and supporting patients with hereditary predispositions. In fact, Siteman leads a registry of patients with known inherited tendencies for colon cancer to better support them and their families.  

When Should I See a Doctor? 

Colorectal cancer often does not cause symptoms in its early stages, which is exactly why regular screenings are important. When symptoms do appear, they can easily be mistaken for common, benign digestive problems and ignored, which can delay diagnosis. 

If you are at average risk, talk with your primary care physician about starting colorectal cancer screening at age 45. If you have a family history, other risk factors, or have noticed symptoms, you may need earlier and more frequent screening. 

Colorectal Screenings at WashU Medicine

Siteman Cancer Center works closely with WashU Medicine’s Division of Gastroenterology to seamlessly connect you to care if you need it. 

WashU Medicine gastroenterologists lead routine screenings and diagnostic colonoscopies. Following these procedures, their team connects patients directly to Siteman experts if they need additional support. You will know the next best step if your screening is abnormal.  

If you have concerns about your colon health, or if you simply want to come in for a routine checkup, you can contact our care coordinators. Our oncology-trained care coordinators – nurses who help with scheduling and navigation – can help you through the process.  

If you are experiencing any of the following symptoms, especially if they are new, persistent, or worsening, make an appointment with your doctor and request a screening.  

Symptoms that need evaluation through screening: 

• Blood in your stool (bright red or very dark) 
• Changes in bowel habits, such as diarrhea, constipation, or narrowing of the stool that last more than 2 weeks 
• A feeling that your bowel doesn’t empty completely 
• Abdominal pain, cramping, or discomfort 
• Rectal pain or pressure 
• Unexplained weight loss 
• Persistent fatigue or weakness 

Experiencing these symptoms does not necessarily mean you have colorectal cancer. Many conditions cause gastrointestinal symptoms, but if symptoms persist, you need to have a physician evaluate you. 
 

Research shows colorectal cancer is on the rise in younger adults. WashU Medicine researchers and scientists are leading studies to learn why. This is called early onset colorectal cancer or young-onset colorectal cancer (YO-CRC). Siteman was one of the first cancer centers in the country to address the needs of this growing population with YO-CRC and open a dedicated program just for them.  

Our experts excel in correctly diagnosing YO-CRC and treating younger patients, even at more advanced stages.  

Learn more about kinds of colorectal cancer screenings

Why Choose Siteman for Your Colorectal Cancer Diagnosis? 

Siteman Cancer Center sets the standard for colorectal cancer diagnosis in the region. As the only NCI-designated Comprehensive Cancer Center in the region, WashU Medicine physicians and pathologists at Siteman are trained in the most advanced diagnostic techniques available.  

If you have received a diagnosis elsewhere or are looking for a second opinion, you can come to Siteman. Many patients in our care have referred themselves directly. To get started, reach out to one of our care coordinators to take advantage of our expertise and treatment options.  

When you come to Siteman for a colorectal cancer diagnosis, our team works to determine: 

• The exact type and location of your cancer  
• If and how far the cancer has spread 
• The genetic and molecular profile of your tumor 

All of this information will directly shape which treatments will work best for you. 

At Siteman, we coordinate your care to create the most benefit for you and the time you are at your diagnostic visit. That means you will often meet with several colorectal specialists on the day of your appointment. This can reduce the total number of appointments you need. Your diagnostic team may include a surgeon, a medical oncologist, a radiation oncologist, and a pathologist, all reviewing your care plan together. 

What to Expect During a Colorectal Cancer Diagnosis 

If you have a screening test that is abnormal, or if your symptoms need further evaluation, your physician will order a series of tests.  

For an accurate colorectal cancer diagnosis, your team may order: 

• Lab work and blood tests 
• Imaging and scans such as CT, MRI, PET-CT, and ultrasound 
• Internal tests including colonoscopy, biopsy, and endoscopic procedures 

Imaging Tests 

Imaging tests create detailed pictures of the inside of your body using sound waves, radiation, or magnetic fields. For colorectal cancer, imaging helps physicians locate the tumor, assess its size, and determine whether cancer has spread to nearby lymph nodes or other organs. 

CT scan: Takes detailed cross-sectional X-ray images of the abdomen and pelvis. Often the first imaging test used after a colorectal cancer diagnosis. 

MRI: Uses magnets to create highly detailed images of soft tissue. Especially important for rectal cancer to assess how deeply the tumor has grown into the rectal wall and nearby structures. 

PET-CT scan: Combines a PET scan (which uses a special sugar solution to detect active cancer cells) with a CT scan. Helps identify whether cancer has spread to distant sites in the body. 

Endorectal ultrasound: A probe inserted into the rectum uses sound waves to create images of the rectal wall. Used specifically for rectal cancer staging to determine how far the tumor has grown. 

Chest X-ray: May be used to check whether colorectal cancer has spread to the lungs. 

Internal Tests 

Internal diagnostic tests allow physicians to directly examine the colon and rectum, and collect tissue samples for analysis. Some require light or complete sedation so you are comfortable during the procedure. 

Colonoscopy: A physician guides a thin, flexible tube with a camera through the colon and rectum. This allows direct visualization of the entire colon lining and the ability to remove polyps or take biopsies during the same procedure. 

Biopsy: A small sample of tissue is removed from the tumor or suspicious area and examined under a microscope by a pathologist. A biopsy is the only way to definitively confirm the presence of cancer. Pathologists conduct genetic sequencing on sample cells to pinpoint mutations.  

Rigid proctoscopy: A rigid scope is used to examine the rectum closely, particularly to assess the exact location and size of a rectal tumor. 

Staging Colorectal Cancer 

Once a diagnosis is confirmed, staging describes how large the tumor is and how far the cancer has spread. Staging is a critical part of the process. It directly determines your treatment options and helps your team set realistic expectations for outcomes. 

Colorectal cancers are staged from 0 to 4, but staging for colon and rectal cancers can be different from each other.  

Cancers caught at earlier stages generally have more treatment options and better outcomes. But even at later stages, Siteman offers advanced care, including clinical trials, that can make a meaningful difference in survivability and quality of life.  

Understanding Colorectal Cancer Stages 

Every treatment plan at Siteman is individualized for you. Your team will evaluate all factors before making a recommendation. Here is what each stage generally means: 

Stage 0 (Carcinoma in situ): Abnormal cells are found only in the innermost lining of the colon or rectum. This is the earliest possible stage and is often treated with local removal during colonoscopy. 

Stage 1: The cancer has grown into the wall of the colon or rectum but has not spread beyond it. Surgery alone is often curative. 

Stage 2: The tumor has grown through the wall of the colon or rectum into nearby tissue, but has not reached lymph nodes. Surgery is the primary treatment, and chemotherapy may be recommended afterward for higher-risk cases. 

Stage 3: The cancer has spread to nearby lymph nodes. Treatment typically involves surgery followed by chemotherapy. For rectal cancer, radiation and chemotherapy before surgery (neoadjuvant therapy or TNT) is often the standard approach. 

Stage 4: The cancer has metastasized, or spread, to other organs,  most commonly to the liver or lungs. Treatment may include chemotherapy, targeted therapy, immunotherapy, surgery for metastatic sites, or enrollment in clinical trials.  

Access to Clinical Trials 

As the only NCI-designated Comprehensive Cancer Center in the region, Siteman offers access to groundbreaking clinical trials that are unavailable elsewhere. With over 100 open trials for colorectal cancer, Siteman patients have access to the latest diagnostic tools and treatment strategies being developed. 

Some trials focus on improving diagnostic precision — for example, identifying genetic mutations that predict how a cancer will behave. Others explore novel therapies for specific tumor profiles. 

Your care team will review your case and identify every clinical trial for which you may be eligible.