Rectal Adenocarcinoma

Rectal adenocarcinoma is a type of cancer that forms in the tissues of the rectum, typically starting as abnormal growths called polyps that develop over many years before becoming cancerous tumors.

Table of contents

• What is rectal adenocarcinoma?
• Where the rectum is located
• Causes and risk factors
• Signs and symptoms
• How it is diagnosed
• Treatment options
• Living with rectal cancer

What is rectal adenocarcinoma?

Rectal adenocarcinoma is the most common type of cancer that starts in the rectum. The rectum is the last several inches of your large intestine, and cancer in this area behaves differently from cancer in other parts of the colon^[1]. Adenocarcinomas are cancers that develop from gland cells in the inner lining of the rectum^[7].

Most rectal cancers begin as clumps of abnormal cells called polyps, also known as adenomas. These polyps are usually not cancerous at first. However, over time—typically 10 to 15 years—some polyps can develop into cancer through an accumulation of genetic changes^[2][5]. This slow development means that regular screening tests like colonoscopies can find and remove polyps before they become cancer, significantly reducing your risk^[2].

Adenocarcinomas make up about 98% of all rectal cancers^[7]. Rectal cancer is the third most common cancer in the digestive system, behind colon cancer and pancreatic cancer. Experts estimate that 46,200 people will receive a rectal cancer diagnosis in 2024^[2].

Where the rectum is located

• Rectum
• Large intestine (colon)
• Anus
• Anal canal

The rectum is part of your body’s digestive system. Your digestive system processes nutrients from food and helps remove waste material from your body. It includes your esophagus, stomach, small intestine, and large intestine^[4].

The colon, also called the large bowel, is the main part of the large intestine and is about 5 feet long. Together, the rectum and anal canal make up the last part of the large intestine and measure 6 to 8 inches long. The anal canal ends at the anus, which is the opening that allows waste to leave your body^[4][6].

Doctors define the start of the rectum in slightly different ways. Surgeons typically consider the rectum to start at the level of the sacral promontory—a bone landmark in your pelvis. Anatomists define it as starting at the level of the third sacral vertebra. Because of these different definitions, the measured length of the rectum varies from 12 to 15 centimeters^[7].

The location of a tumor within the rectum matters for treatment decisions. Doctors classify rectal cancers as low (up to 5 cm from the anal opening), medium (5 to 10 cm), or high (10 to 15 cm)^[7].

Causes and risk factors

The exact cause of rectal cancer is unknown. What researchers do know is that cancer develops when cells in the rectum undergo certain changes in how they function, especially in how they grow and divide^[4]. Many risk factors don’t directly cause cancer but instead increase the chance of DNA damage in cells that may eventually lead to cancer^[4].

Several factors can increase your risk of developing rectal cancer^[2][4]:

• Age: Like most cancers, the risk of rectal cancer increases as you get older. The average age at diagnosis is 63 years^[2].
• Family history: If you have a parent, sibling, or child who has been diagnosed with rectal cancer, your chance of developing it is almost double^[2].
• Personal health history: Having had colon, rectal, or ovarian cancer before increases your risk. A history of large colorectal polyps (1 centimeter or larger) or polyps with abnormal-looking cells also raises your risk^[4].
• Inflammatory bowel disease: Having chronic ulcerative colitis or Crohn’s disease for 8 years or more increases your risk^[2][4].
• Inherited genetic conditions: Several inherited conditions significantly increase rectal cancer risk, including Lynch syndrome (also called hereditary nonpolyposis colorectal cancer), familial adenomatous polyposis (FAP), MUTYH-associated polyposis (MAP), juvenile polyposis syndrome (JPS), Peutz-Jeghers syndrome, and PTEN hamartoma tumor syndrome^[2][4].
• Diet: People who eat a lot of red meat and processed meat have a higher risk of developing rectal cancer^[2].
• Alcohol consumption: Having three or more alcoholic drinks per day increases your risk^[4].
• Smoking: People who smoke cigarettes are more likely to develop and die from rectal cancer than people who don’t smoke^[2][4].
• Obesity: People who have obesity are more likely to develop rectal cancer compared to people who don’t^[2].
• Race: Statistically, people who are Black are more likely to develop rectal cancer, though the reasons for this aren’t fully understood yet^[2][4].
• Sex: Men are slightly more likely to develop rectal cancer than women^[2].

Having one or more of these risk factors doesn’t mean you will definitely get rectal cancer. Many people with risk factors never develop the disease, while others with no known risk factors do^[4].

Signs and symptoms

You can have rectal cancer for years without noticing any changes in your body. In many cases, rectal cancers don’t cause symptoms at all, especially in the early stages. Symptoms usually appear when the disease is more advanced^[1][2].

Common symptoms of rectal cancer include^[1][2][4][6]:

• Rectal bleeding: Blood in your stool that may look bright red or dark maroon in color
• Changes in bowel habits: Diarrhea, constipation, or needing to pass stool more frequently than usual
• Feeling that your bowel doesn’t empty completely after you go to the bathroom
• Narrow stools: Poop that looks stringy or as thin as a pencil
• Abdominal pain: General discomfort in your belly, including frequent gas pains, bloating, fullness, or cramps
• Unexplained weight loss: Losing weight without trying
• Tiredness and weakness
• A lump in the rectum that may be found during a medical exam
• Change in appetite

These symptoms can also be caused by many other conditions besides rectal cancer. However, if you experience any of these signs, you should check with your doctor^[4][6].

How it is diagnosed

Rectal cancer is often found during routine screening tests or when symptoms prompt further investigation. Diagnosis typically begins with a careful medical history and physical examination, including a digital rectal exam, where the doctor inserts a gloved finger into the rectum to feel for lumps or anything unusual^[5][6].

Several tests and procedures are used to diagnose rectal cancer^[2][6][10]:

Colonoscopy: This is the main test used to examine the rectum and colon. A long, flexible tube with a camera at the end, called a colonoscope, is inserted into the anus to view the inside of the large intestine. Your healthcare professional looks for signs of cancer and can take tissue samples during this procedure. Medicines are given before and during the procedure to keep you comfortable^[6][10].

Rigid sigmoidoscopy: This examination is important to measure the exact distance from the tumor to the anal opening, which helps determine treatment options^[5].

Biopsy: During a colonoscopy or sigmoidoscopy, your doctor removes a very small sample of tissue from inside the rectum. This tissue is sent to a laboratory where specialists examine it under a microscope to look for cancer cells. Special tests on the tissue sample provide detailed information about the cancer that helps guide treatment decisions^[10].

Once rectal cancer is diagnosed, additional tests determine how far the cancer has spread. These staging tests include^[2][10]:

• Blood tests: A complete blood count (CBC) shows the numbers of different types of cells in your blood. Tests for CEA (carcinoembryonic antigen), a tumor marker, may also be done
• CT scans (computed tomography): These create detailed pictures of your chest, abdomen, and pelvis to check if cancer has spread to other organs
• MRI (magnetic resonance imaging): An MRI of the pelvis can accurately show how deeply the tumor has grown into the rectal wall and whether nearby lymph nodes are affected
• Transrectal ultrasound: This test uses sound waves to create images and can also show the extent of tumor growth and lymph node involvement
• PET scan: This imaging test may be used in certain cases to look for cancer spread throughout the body

Treatment options

Treatment for rectal cancer often differs from treatment for colon cancer because the rectum sits in a tight space very close to other organs and structures, making surgery more complex^[1]. Your treatment depends on several factors, including where the tumor is located in the rectum, how far the cancer has spread, and your overall health^[11].

Main treatment approaches include^[1][11]:

Surgery: Surgery to remove the cancer is the primary treatment for rectal cancer. For small, early-stage cancers, surgeons may perform a local excision to remove just the tumor and a small amount of surrounding tissue. For larger cancers, more extensive surgery is needed to remove part of the rectum along with nearby lymph nodes. In many cases, surgeons can perform sphincter-sparing procedures that preserve normal bowel function. However, some patients may need a colostomy, where the end of the colon is brought through an opening in the abdomen to collect waste in a bag^[11].

Radiation therapy: Radiation therapy uses high-energy waves to kill cancer cells. For rectal cancer, radiation is often given before surgery to shrink the tumor, making it easier to remove. This approach can also reduce the chance of cancer coming back^[1].

Chemotherapy: Chemotherapy uses drugs to kill cancer cells throughout the body. Common drugs used for rectal cancer include fluorouracil, capecitabine, oxaliplatin, and irinotecan. Chemotherapy may be given before surgery, after surgery, or both^[1].

Chemoradiotherapy: Treatment that combines chemotherapy and radiation therapy together is called chemoradiotherapy. This approach is commonly used before surgery for rectal cancer to shrink tumors and improve outcomes^[1].

Targeted therapy: These are newer treatments that target specific features of cancer cells. They may be used for advanced rectal cancer^[1].

Immunotherapy: This type of treatment helps your immune system fight cancer. It may be an option for some patients with certain genetic features in their tumors^[1].

Response to treatment and the stage of cancer at diagnosis are the most important factors that influence outcomes. Doctors measure response by examining how much the tumor has shrunk or disappeared after treatment^[5].

Living with rectal cancer

Living with rectal cancer involves more than just medical treatments. Cancer affects your whole life—including what you eat and drink, your physical activity, your emotional health, and your relationships^[18].

Follow-up care: After treatment, regular follow-up appointments are essential to monitor for cancer recurrence and manage any long-term effects. Your doctor will recommend a schedule for check-ups, which typically includes colonoscopy exams, blood tests to check CEA levels, and imaging tests such as CT scans. For rectal cancer patients who had certain types of surgery, additional procedures like proctoscopy may be needed every few months during the first years after treatment^[17].

Managing side effects: Treatment for rectal cancer can cause various side effects. Since treatments often affect the digestive system, many people experience bowel changes such as diarrhea, constipation, or loss of bowel control. Working with your healthcare team, including dietitians, can help you manage these challenges through diet adjustments, medications, and bowel retraining techniques^[17].

Nutrition and diet: What you eat matters both during and after treatment. Research shows that patients who maintain good nutrition don’t only experience better quality of life but may also see improved treatment outcomes. Eating a balanced diet with fiber-rich foods, staying hydrated, and working with registered dietitians can help you manage symptoms and support your recovery^[18].

Exercise: Physical activity has been proven to improve treatment outcomes, reduce fatigue, and boost mental health. There are many benefits to getting your body moving, and various ways to exercise depending on your abilities and preferences^[18].

Emotional support: A cancer diagnosis naturally triggers difficult emotions and questions about the future. Many people find support groups helpful—connecting with others who are facing similar challenges can provide new coping strategies and reduce feelings of isolation. Counseling services and mental health support are also available to help you manage anxiety, depression, and fears about recurrence^[16][19].

Creating a survivorship care plan: Work with your doctor to develop a comprehensive care plan that includes your follow-up schedule, awareness of potential long-term side effects, recommendations for maintaining overall health through nutrition and exercise, and guidelines for cancer screening. Having a clear plan can help you feel more in control of your health^[17].

Remember that this is your body and you have the right to make decisions about your care. Don’t forget that there’s still life between treatments—visit with family members, do things you love, and make moments count^[16].