Colon Cancer Signs and Symptoms: What to Watch For and When to See a Surgeon

Early Signs of Colon Cancer

Early colon cancer often causes no symptoms at all. When symptoms do appear, they tend to be subtle and easy to attribute to diet, hemorrhoids, or stress. The changes that most often turn out to be significant are:

• A change in bowel habits that lasts more than a few weeks: new constipation, new diarrhea, or alternating between the two
• Narrower stools than usual, sometimes described as pencil-thin
• Blood in or on the stool, which may be bright red or dark and tarry
• A feeling that the bowel does not empty completely after a movement
• Persistent abdominal discomfort: cramps, gas, bloating, or a dull ache
• Unexplained fatigue, often from slow blood loss and anemia
• Unintended weight loss

None of these symptoms is specific to cancer. Each has more common, benign causes. What should prompt evaluation is persistence: symptoms that last beyond two to three weeks, or that keep coming back, are the ones to have checked rather than watched.

Symptoms That Depend on Where the Cancer Is

Right-sided (ascending) colon

The right side of the colon is wide, and stool there is still liquid, so tumors can grow large without blocking anything. Cancers here often cause slow, hidden bleeding that leads to iron-deficiency anemia. The first clue may be fatigue, shortness of breath on exertion, or a low blood count on a routine test, with no visible blood in the stool at all.

Left-sided (descending and sigmoid) colon

The left colon is narrower and stool is formed, so tumors here are more likely to change bowel habits, narrow the stool, and cause visible bright-red blood, cramping, or a sense of incomplete emptying.

Rectum

Rectal cancers commonly cause bright-red bleeding, a persistent urge to pass stool, and changes in stool shape. Because rectal bleeding is so often caused by hemorrhoids, it is frequently dismissed. Bleeding that is new, persistent, or occurs in someone over 40 should be evaluated even when hemorrhoids are present.

Warning Signs That Need Prompt Attention

Some symptoms suggest that a tumor is blocking the bowel or has caused significant blood loss. Seek care promptly, or go to the emergency department, for:

• Severe or worsening abdominal pain with bloating
• Inability to pass stool or gas, with nausea or vomiting
• Heavy rectal bleeding or passing large clots
• Black, tarry stools
• Dizziness, rapid heartbeat, or fainting, which can signal anemia or bleeding
• Rapid, unexplained weight loss

Who Is at Higher Risk

Anyone can develop colon cancer, but several factors raise the likelihood:

• Age. Risk rises steadily after 45, although rates in younger adults have been increasing for two decades.
• Personal history of colorectal polyps (especially adenomas) or a previous colorectal cancer.
• Family history of colorectal cancer or advanced polyps in a first-degree relative, particularly before age 60.
• Inherited syndromes such as Lynch syndrome or familial adenomatous polyposis (FAP).
• Inflammatory bowel disease: long-standing ulcerative colitis or Crohn's colitis.
• Lifestyle factors: a diet high in red and processed meat and low in fiber, obesity, physical inactivity, smoking, and heavy alcohol use.
• Type 2 diabetes.

People with a family history or an inherited syndrome usually need earlier and more frequent screening than the general population, and this is worth discussing with a physician even before any symptoms appear.

Why Screening Matters Even Without Symptoms

Most colon cancers begin as a polyp, a small growth on the inner lining of the colon, that takes years to turn cancerous. Screening finds and removes polyps before that happens, and finds cancers at an early, curable stage. The U.S. Preventive Services Task Force recommends that adults at average risk begin screening at age 45 and continue through 75, with individualized decisions from 76 to 85.

Screening options include:

• Colonoscopy, typically every 10 years if normal. It examines the whole colon and allows polyps to be removed at the same time.
• Stool-based tests such as the fecal immunochemical test (FIT) every year, or a stool DNA test every one to three years. A positive result must be followed by a colonoscopy.
• CT colonography or flexible sigmoidoscopy at set intervals.

The best test is the one that actually gets done. If you are 45 or older and have never been screened, that is the single most useful step you can take, regardless of symptoms.

How Colon Cancer Is Diagnosed

Colonoscopy and biopsy

When symptoms or a positive screening test raise concern, a colonoscopy is the definitive next step. A flexible camera examines the full length of the colon, and any suspicious area is biopsied. The biopsy confirms whether cancer is present and what type.

Blood tests

A complete blood count checks for anemia. A CEA (carcinoembryonic antigen) level is often measured as a baseline; it is not a screening test but is useful for follow-up after treatment.

Imaging and staging

Once cancer is confirmed, a CT scan of the chest, abdomen, and pelvis determines whether it has spread to lymph nodes, the liver, or the lungs. For rectal cancer, an MRI of the pelvis or endorectal ultrasound shows how deeply the tumor has grown. Together these tests establish the stage, from stage I (confined to the inner layers of the bowel wall) to stage IV (spread to distant organs), which guides treatment.

Treatment Options

Surgery

Surgery is the primary treatment for most colon cancers that have not spread widely. The operation, a colectomy, removes the segment of colon containing the tumor along with its blood supply and nearby lymph nodes, then reconnects the healthy ends. Depending on the tumor's location this may be a right, left, sigmoid, or extended colectomy. Most colectomies can be performed laparoscopically or robotically through small incisions, which typically means less pain and a faster recovery than open surgery. Some very early cancers within a polyp can be removed entirely during colonoscopy.

Chemotherapy

Recommended after surgery for many stage III cancers and some higher-risk stage II cancers to reduce the chance of recurrence, and used as the main treatment when cancer has spread to distant organs.

Radiation therapy

Used mainly for rectal cancer, often combined with chemotherapy before surgery to shrink the tumor.

Targeted therapy and immunotherapy

Options for certain advanced cancers, selected based on the tumor's genetic features.

Treating cancer that has spread to the liver

Colon cancer that has spread to the liver can sometimes still be treated with intent to cure, by removing or ablating the liver tumors in addition to the primary cancer. This is where a surgeon trained in both colorectal and liver surgery is particularly valuable. Learn more on our liver cancer and surgical oncology pages.

When to See a Surgeon

A primary care physician or gastroenterologist is usually the first stop for symptoms and for screening. A surgical consultation is appropriate once a cancer or a polyp too large to remove endoscopically has been found, or when a patient wants to understand what an operation would involve before deciding on treatment.

Dr. Murtaza Shakir is board certified in both General Surgery and Complex General Surgical Oncology, with fellowship training at the University of Pittsburgh Medical Center that included colorectal and liver cancer surgery. He evaluates patients with newly diagnosed colon and rectal cancer at the Katy and Sugar Land offices and coordinates care with gastroenterologists and medical oncologists. See our colon cancer surgery page and meet Dr. Shakir.

What Recovery Looks Like After Colon Surgery

After a laparoscopic or robotic colectomy, most patients stay in the hospital for two to four days, walking from the first day and returning to a light diet as bowel function recovers. Open surgery generally involves a longer stay. Desk work is often possible within two to three weeks; heavy lifting is limited for about six weeks. Bowel habits may take several weeks to settle, and a temporary or, less commonly, permanent stoma is needed in some rectal cancer operations, which is discussed in detail beforehand. Our pre-operative and post-operative care pages cover general preparation and recovery.

Follow-up after treatment includes regular visits, CEA blood tests, CT scans, and a repeat colonoscopy, typically at one year and then at intervals, to catch any recurrence or new polyps early.

Final Takeaway

Colon cancer is common, slow-growing, and very treatable when caught early. Two habits make the difference: get screened from age 45, and do not wait out bowel changes or bleeding that last more than a few weeks. If a cancer or a large polyp is found, a consultation with a surgical oncologist will clarify the stage, the treatment plan, and what surgery and recovery would involve. Patients across Katy, Sugar Land, Richmond, Fulshear, and West Houston can request a consultation at either of our two Fort Bend County offices.

Frequently Asked Questions

References

1. U.S. Preventive Services Task Force. Colorectal Cancer: Screening - Final Recommendation Statement (2021). uspreventiveservicestaskforce.org.
2. National Cancer Institute. Colorectal Cancer - Patient Version. cancer.gov.
3. National Comprehensive Cancer Network. NCCN Guidelines for Patients: Colon Cancer; Rectal Cancer; Colorectal Cancer Screening. nccn.org.
4. American Cancer Society. Cancer Types: Colorectal Cancer. cancer.org.
5. American College of Surgeons. Surgical Patient Education: Operations and Procedures. facs.org.