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Warning Signs of Colorectal Cancer (+ Risk Factors and Lab Tests for Detection)

Medically Approved by Dr. Edward Salko

Table of Contents

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The information in this article is not intended to replace professional medical advice, diagnosis, or treatment. Instead, consult your physician or any licensed healthcare providers if you have questions.

Symptoms of colorectal cancer often show up at later stages. In several cases, when these symptoms are recognized, the treatment for the condition becomes complex, affecting the mortality rate. Still, there are CRC warning signs you can watch out for, such as sudden weight loss, recurring abdominal pain, bloody stool, and bloating. Find out how these conditions may indicate colorectal cancer. 

  1. Unexplained Weight Loss

Unintentional weight loss can be due to several factors, including a malignant tumor forming in the colorectal area. The cancer cells can alter metabolism, acquiring more energy during rest, which leads to significant weight loss. This particular change can be observed in all stages of cancer. 

Nonetheless, the driving elements behind this type of weight reduction are the location, size, and depth of the tumor. For these reasons, unexplained weight loss, especially in the absence of purposive dietary alteration and increased physical activities, has become a significant prognostic criterion in assessing colorectal cancer. 

In addition, cancer may also cause cachexia, a metabolic syndrome that can suppress appetite and result in muscle mass loss. You might notice sudden appetite loss, especially when symptoms of colon cancer and rectal cancer include nausea and stomach pain. 

  1. Persistent Abdominal Pain

Colorectal cancer is also characterized by persistent, vague abdominal cramps. It can be permanent or intermittent and can vary in intensity–these depend mainly on the tumor size and its exact location in the colon. 

If the cancer cell has spread outside its point of origin (metastasis), the pain can extend in the direction of its expansion. In addition, the growing tumor can also put pressure on nearby tissues, exacerbating the pain. 

Keep in mind, however, that abdominal pain can be due to other factors or conditions. With that in mind, it’s important to seek medical advice to rule out any serious underlying conditions and verify its association with cancer.

  1. Changes in Bowel Habits

Changes in bowel habits may also indicate colorectal cancer. In more advanced stages, when the tumor has grown in size, it could obstruct the colon or rectum, affecting defecation. These changes may include diarrhea, constipation, or incomplete bowel movements. 

Discuss any significant changes to your bowel habits with your doctor if they persist for over a few days. In terms of diagnosis, studies have shown that bowel habit changes do not yield enough value to be considered a significant criterion for the assessment, especially among people below the age of 55. 

  1. Blood in Stool

While blood in the stool can have various causes, including hemorrhoids or anal fissures, it can also be a sign of colorectal cancer. Some cases of this cancer start from the development of polyps in the colon. Polyps are typically harmless and merely protrusions in the intestinal wall, but as they grow, they can bleed. 

Polyps can become cancerous due to mutations triggered by genetic factors. In this case, their growth speeds up, exacerbating the bleeding. However, it’s imperative to note that polyps have a 5% to 10% chance of malignancy

Hence, rectal bleeding or blood in the stool can also be associated with the tumor itself. It could happen gradually, and the blood may not be visible to the naked eye (occult blood). 

Pro tip: As blood in the stool may not be noticeable in colorectal cancer, immunoassay tests such as the fecal occult blood test are typically requested to confirm bleeding. But if you’re able to observe the visible presence of blood, it’s crucial to learn the next steps to address colorectal bleeding
  1. Permanent Bloating or Gas

During colorectal cancer, the tumor can cause fluid to build up in the abdomen, causing bloating and gas. Also, constipation, diarrhea, abdominal cramping, and nausea associated with colorectal cancer can cause bloating.

If you observe frequent gas and a stomach that doesn’t seem to deflate despite applying common home remedies to bloating, consult your doctor and make sure to take note of other glaring symptoms as well. 

Risk Factors of Colorectal Cancer

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Your risk of developing colon and rectal cancers depends on combined factors that include your genetic disposition and habits. If you tick the boxes for the following cases, consult your healthcare provider to assess your risk level. 


People aged 50 and above have a higher susceptibility to forming colorectal cancer. As with other age-related conditions, your big intestine lining and rectal tissue tend to become worn out, and your metabolism can drastically alter. These increase your chances of developing colon polyps. 

Family History

Your chances of having colon or rectal cancer spike up if you have someone in the family diagnosed with the condition. Make sure to inform your physician if this is the case to accurately measure your vulnerability.

Inflammatory Bowel Disease (IBD)

Studies have shown that individuals with IBD have a higher chance of forming CRC due to the pro-neoplastic impact of the inflamed intestinal lining. Tumors developed proximal to the colon as a result of IBD have an increased likelihood of becoming malignant. 

Lifestyle Choices

Poor diet, lack of exercise, and overconsumption of alcohol and tobacco products are the most notable lifestyle factors that influence CRC risk. The lack of dietary fiber, in particular, and the high intake of fats and proteins can directly impact the function of your intestinal and rectal tissues. 

Lab Tests for Early Detection of CRC Cancer

Colorectal cancer can be detected and diagnosed with various lab tests. These tests help diagnose people with symptoms as well as screen people who don’t have symptoms. The following are the main lab tests for colorectal cancer:

Colonoscopy: The Gold Standard for Diagnosing Colorectal Cancer

When it comes to diagnosing colorectal cancer, colonoscopy is the gold standard. This procedure involves inserting a flexible tube with a camera into the rectum and guiding it through the colon. The doctor can check for polyps or tumors along the entire colon length. In case of suspicious growths, they can be biopsied or removed for more testing. Colonoscopy for cancer is usually recommended for people over 50 or those at higher risk based on family history.

Other Diagnostic Tests for Colorectal Cancer

Other lab tests besides colonoscopies can help detect and diagnose colorectal cancer. These tests include:

  • Fecal Occult Blood Test (FOBT): This test detects small traces of blood in the stool that are not visible to the naked eye, which may indicate colorectal cancer or other gastrointestinal conditions.
  • Genetic Tests: Genetic tests can determine if an individual has inherited certain genetic mutations that predispose them to colorectal cancer, such as Lynch syndrome or FAP. Patients with a strong family history of colorectal cancer or those who have been diagnosed with the disease at an early age will typically benefit from these tests.

How Doctors Treat Colorectal Cancer

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Treatment for colorectal cancer will depend on the stage, location, and other factors. For this reason, you may need a team of doctors working together to eradicate the cancerous tumor, especially if the cancer has metastasized.

The procedures involved in cancer treatment may include surgery, ablation, radiation therapy, chemotherapy, immunotherapy, and targeted therapy drugs. Your team of doctors may consist of a gastroenterologist and various oncologists, along with surgeons. 

Naturally, if the cancer has progressed, additional medical treatment may be necessary. It’s crucial to detect colorectal cancer at its early stages not just for its lower mortality rate but also because it ensures simplified procedures. 

For example, patients diagnosed with stage 1 colon cancer may undergo polyp removal during colonoscopy. If the cancer cells are completely removed surgically, there’s a chance that you may not need to go through additional procedures. However, these all depend on several factors that your doctor will take into account.

On the other hand, stage 4 colon cancer may require more complex treatment since the mutated cells have spread to the nearby organs–most commonly the liver and nearby lymph nodes. In this case, you may have to undergo chemotherapy and other treatment options on top of surgery.

If your liver has been reached by the cancer cells, embolization may be needed. An embolization is a minimally invasive medical procedure that closes off blood vessels supplying tumors with substances called embolic agents. 

Frequently Asked Questions

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How does colorectal cancer begin?

Colorectal cancer can develop from polyps growing in the intestinal lining down to the rectum. While polyps are generally non-cancerous, they can mutate into malignant cells if you have a high risk of developing cancer in your big intestine and rectum. This risk can be traced back to your family history, age, diet, and pre-existing bowel problems.

Can colorectal cancer be cured?

There is no singular treatment for colorectal cancer, and the condition still lacks a definitive cure. However, chemotherapy and surgery may increase the chances of survival depending on the cancer stage, the location of the tumor, and the compatibility and response of the patient to the treatment. Nonetheless, early detection remains an essential step in lowering the mortality rate. Therefore, it’s critical to undergo screening following your colorectal cancer risk assessment. 

How can you prevent colon cancer?

You can protect yourself from colon and rectal cancer by undergoing screening through colonoscopy and blood tests, especially if you’re already at risk, such as when you reach the age of 50. But even as a young person, you can start preventing colorectal cancer by eating healthy, limiting alcohol intake, maintaining optimum weight, avoiding smoking, and learning about your family’s medical history. 

The Bottom Line

While the warning signs of colorectal cancer are similar to other common medical conditions involving digestion and nutrient absorption, it’s crucial not to take them for granted. Notable symptoms for colorectal cancer, which mainly are grave versions of the abovementioned warning signs, may not be observed until the cancer is already at a higher stage. If you are at high risk for colon or rectal cancer, make sure to undergo screening and avoid habits that could trigger mutation.

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