Rectal Adenocarcinoma (Rectal Cancer)

Why rectal cancer is treated differently from colon cancer

Rectal and colon cancers are both colorectal cancers and share causes, but the rectum lies in the narrow pelvis close to the sphincter muscles, bladder, sexual organs and nerves. This makes surgery harder and raises the risk of cancer returning locally. As a result, rectal cancer is staged with pelvic MRI and often treated with chemotherapy and radiation before surgery. For cancers anywhere in the intestines, see intestinal cancer.

Symptoms

• rectal bleeding: bright or dark red blood on or mixed with stool
• tenesmus: feeling the need to pass stool even after emptying
• changes in bowel habits: constipation, diarrhea, or more frequent movements
• narrow or ribbon-like stools
• mucus in the stool
• rectal or pelvic pain (usually later)
• fatigue and breathlessness from iron deficiency anemia
• unexplained weight loss

Bleeding is often mistaken for hemorrhoids. Persistent bleeding should be evaluated with a colonoscopy or sigmoidoscopy.

Risk factors

• age over 50 (but rising in younger adults)
• personal or family history of colorectal cancer or adenomatous polyps
• Lynch syndrome, familial adenomatous polyposis
• inflammatory bowel disease
• obesity, inactivity, smoking and heavy alcohol use
• diet high in red and processed meats and low in fiber
• type 2 diabetes

Diagnosis and staging

1. Digital rectal exam: can feel low tumors.
2. Colonoscopy with biopsy: confirms adenocarcinoma and checks the rest of the colon.
3. Pelvic MRI: shows tumor depth, lymph nodes, the distance to the sphincter and the circumferential resection margin, which guides treatment.
4. CT of the chest, abdomen and pelvis: looks for spread to the liver and lungs.
5. CEA blood test: a tumor marker for follow-up.
6. Tumor testing for mismatch repair (MMR) or microsatellite instability (MSI): identifies Lynch syndrome and tumors that respond to immunotherapy.

Stages

Treatment

Early-stage cancer (stage I)

• Local excision: some very early tumors are removed through the anus (transanal surgery).
• Total mesorectal excision (TME): removal of the rectum with its surrounding fatty tissue and lymph nodes. Procedures include low anterior resection (keeping the anus) and abdominoperineal resection (removing the anus, with a permanent colostomy) for very low tumors.

Locally advanced cancer (stage II and III)

• Total neoadjuvant therapy (TNT): chemotherapy and radiation (short-course or long-course chemoradiation) given before surgery. This shrinks tumors, reduces local recurrence and increases the chance of a complete response.
• Surgery (TME) after neoadjuvant treatment, often with a temporary ileostomy.
• Watch and wait: if the tumor completely disappears on exam, endoscopy and MRI after treatment (clinical complete response), some patients can avoid surgery with very close surveillance. Regrowth occurs in a minority and is usually still treatable with surgery.

Mismatch repair-deficient rectal cancer

A small proportion of rectal cancers are MMR-deficient. Clinical trials of immunotherapy (such as dostarlimab) in this group have shown complete disappearance of tumors in nearly all patients treated, allowing many to avoid radiation and surgery. Testing for MMR status is therefore essential.

Advanced cancer (stage IV)

Chemotherapy, targeted therapy (based on KRAS, NRAS, BRAF and HER2 status) and immunotherapy for MSI-high tumors. Surgery or local treatments for limited liver or lung metastases can be curative in some patients.

Side effects and life after treatment

• Bowel function changes: low anterior resection syndrome (urgency, frequency, fragmentation, incontinence) is common after rectal surgery and often improves over 1 to 2 years. Pelvic floor therapy and medicines help.
• Stoma: temporary or permanent; stoma nurses provide training and support.
• Sexual and urinary effects from nerve and radiation effects.
• Fertility: radiation can affect fertility and ovarian function; discuss options before treatment.

Follow-up usually includes CEA tests, CT scans and colonoscopy for at least 5 years.

Outlook

The 5-year relative survival for rectal cancer is about 90% for localized disease, around 74% when spread to nearby lymph nodes or tissues, and lower when spread to distant organs, according to American Cancer Society data. Outcomes continue to improve with modern multimodal treatment.

Prevention and screening

Screening from age 45 with a FIT stool test or colonoscopy finds early cancers and removes polyps before they become cancer. Staying active, avoiding smoking, limiting alcohol and processed meat, and eating fiber-rich foods lower risk.

Frequently asked questions

What are the first symptoms of rectal cancer?

Early rectal cancer may have no symptoms. The most common first symptom is rectal bleeding. Others include a change in bowel habits, narrow stools, mucus, a feeling of incomplete emptying and tiredness from anemia.

Is rectal cancer the same as colon cancer?

Both are colorectal cancers and are usually adenocarcinomas, but rectal cancer is in the last part of the bowel, inside the pelvis. This location means it is staged with MRI and often treated with chemotherapy and radiation before surgery, unlike most colon cancers.

Can rectal cancer be cured without surgery?

Sometimes. If a tumor completely disappears after chemotherapy and radiation, some patients can follow a "watch and wait" approach with close monitoring. People with mismatch repair-deficient tumors may be cured with immunotherapy alone in some cases.

Will I need a colostomy for rectal cancer?

Not always. Many people keep normal bowel continuity, sometimes with a temporary ileostomy that is reversed later. A permanent colostomy is usually needed only when the tumor is very close to or involves the anal sphincter.

What is the survival rate for rectal cancer?

When found while still confined to the rectum, about 90% of people are alive 5 years later. Survival is lower when cancer has spread to lymph nodes or distant organs, but treatment has improved significantly and some people with limited spread are cured.