Anal Cancer: Symptoms, Causes, and Treatment

Anal cancer is a rare type of cancer that accounts for about 2% of gastrointestinal cancers, with roughly 10,930 new cases expected in 2025 in the United States1 . Most anal cancers are highly curable when detected early, with a five-year survival rate of about 85% for localized disease2 . Treatment advances, especially the use of combined chemotherapy and radiation, have significantly improved outcomes for patients3 .

Types of Anal Cancer

Anal cancer originates from different types of cells lining the anal canal and perianal skin. The majority of anal cancers (approximately 85–90%) are squamous cell carcinomas, which arise from the squamous epithelium of the anal canal and can invade underlying tissues4 56. These cancers are often linked to persistent infection with high-risk human papillomavirus (HPV) types, particularly HPV-163 7.

Other less common types include:

• Adenocarcinoma: Originates from glandular cells in the anal canal or anal glands. These tumors are rare and often diagnosed at a later stage due to their location and rarity8 9.
• Melanoma: Arises from melanocytes located in the perianal skin. Anal melanoma is a rare malignancy and is usually detected late because it is difficult to see10 11.
• Basal Cell Carcinoma: A skin cancer type that rarely affects the perianal area and is primarily managed by surgical excision. It more commonly occurs in sun-exposed skin such as the face and hands10 .

Anal cancers are sometimes classified based on their location:

• Anal canal cancers: Begin above the anal verge inside the anal canal.
• Perianal skin cancers: Occur on the skin around the anus, previously called cancers of the anal margin12 .

Anal Cancer Symptoms

Symptoms of anal cancer often resemble those of benign anal conditions, making early diagnosis challenging. Common signs include:

• Rectal bleeding, which is often continuous and more severe than bleeding from hemorrhoids13 1415.
• Anal discharge, including mucus or pus13 14.
• A palpable mass or lump in the anal region13 14.
• Anal or perianal pain or discomfort13 14.
• Changes in bowel habits, such as constipation or urgency13 14.
• Inguinal lymphadenopathy (swollen lymph nodes in the groin), indicating possible regional spread13 14.

About 20% of patients may be asymptomatic at diagnosis, especially in early stages before local invasion or metastasis13 14. The accessibility of the anal canal allows for physical examination, which can aid early detection13 14.

Anal Cancer Causes and Risk Factors

Anal cancer develops when cells in the anal canal or perianal skin undergo genetic mutations that disrupt normal cell growth and death. These mutations affect genes regulating cell proliferation and apoptosis, leading to uncontrolled cell growth and tumor formation16 3. Although the exact triggers for these mutations are not fully understood, several risk factors have been identified.

Risk Factors

• Human Papillomavirus (HPV) Infection: Over 90% of anal cancers are associated with HPV infection, especially high-risk types like HPV-16. Oncogenic HPV proteins E6 and E7 interfere with tumor suppressors p53 and Rb, promoting carcinogenesis3 717.
• Multiple Sexual Partners: Having many sexual partners increases exposure to HPV and HIV infections, raising anal cancer risk3 4.
• HIV Infection and Immunosuppression: HIV weakens the immune system, reducing the body's ability to clear HPV infections and increasing the risk of anal cancer3 4.
• Age Over 50: Anal cancer is more common in older adults, with the median age at diagnosis around 64 years3 181.
• Gender and Race: Higher incidence rates are observed in white females and Black males3 181.
• Smoking: Tobacco use increases the risk of anal cancer19 .
• History of Genital Cancers: Individuals with cervical, vulvar, or vaginal cancer have an increased risk19 .
• Weakened Immune System: Conditions or medications that suppress immunity, such as organ transplant drugs, elevate risk19 .

Diagnosing Anal Cancer

Diagnosis begins with a clinical evaluation, including a detailed history and physical examination3 5. Key diagnostic steps include:

• Digital Rectal Exam (DRE): A gloved, lubricated finger is inserted into the anus to feel for masses or irregularities in the anal canal and rectum3 520.
• Anoscopy: A thin, flexible tube with a light (anoscope) is used to directly visualize the anal canal and distal rectum3 521.
• Proctoscopy: Provides a more extensive view of the rectum compared to anoscopy3 5.
• Biopsy: Tissue samples are obtained during anoscopy or proctoscopy for histopathological confirmation of cancer3 5.
• Imaging: MRI and CT scans are essential for staging the cancer, assessing tumor size, local invasion, and lymph node involvement22 323.

Staging is crucial for treatment planning and prognosis. The stages range from I (small tumor confined to the anal canal) to IV (cancer spread to distant organs) 191.

Anal Cancer Treatment Options

Treatment depends on the cancer type, stage, tumor size, and patient health. The main treatment modalities include chemoradiation, surgery, immunotherapy, and clinical trial options.

Chemoradiation

Concurrent chemoradiation, combining chemotherapy and radiation therapy, is the standard treatment for most anal cancers3 621. Chemotherapy uses drugs to kill cancer cells, while radiation therapy uses high-energy beams to target tumors. This combination enhances the effectiveness of treatment and often avoids the need for surgery3 6.

Radiotherapy can be delivered externally or via brachytherapy (internal radiation) to precisely target the tumor3 6. Treatment schedules are tailored based on tumor characteristics and patient tolerance.

Surgery

Surgery is typically reserved for:

• Small, well-defined tumors that may be removed by local excision without damaging the anal sphincter muscles3 621.
• Salvage therapy for cancers that do not respond to chemoradiation or recur3 6.

In advanced cases, an abdominoperineal resection (APR) may be performed, removing the anus, rectum, and part of the colon, followed by a permanent colostomy3 21.

Immunotherapy

For advanced anal cancer not amenable to chemoradiation or surgery, immunotherapy may be used to help the immune system recognize and attack cancer cells. It is often combined with chemotherapy to improve outcomes, although it is generally not curative but can prolong survival and improve quality of life3 21.

Clinical Trial Treatments

Ongoing clinical trials explore novel therapies and combinations to improve survival and reduce side effects. Patients may consider participation in trials as part of their treatment plan under specialist guidance3 .

Anal Cancer Prevention Strategies

Complete prevention of anal cancer is not currently possible due to incomplete understanding of all causes3 24. However, several strategies can reduce risk:

• HPV Vaccination: Effective in preventing infection with high-risk HPV types linked to anal cancer3 7.
• Safe Sexual Practices: Using condoms and limiting the number of sexual partners reduce HPV and HIV transmission3 419.
• Smoking Cessation: Avoiding tobacco lowers the risk of anal and other cancers19 .
• Regular Screening: High-risk individuals, especially those with HIV or prior HPV infections, should undergo regular medical surveillance, including digital rectal exams and possibly anal Pap tests3 2420.
• Effective HIV Treatment: Antiretroviral therapy in HIV-positive individuals decreases anal cancer risk by improving immune function3 4.

Potential Complications

Treatment for anal cancer can lead to several complications:

• Radiation Proctitis: Inflammation of the rectal mucosa causing pain, bleeding, and irritation25 6.
• Chemotherapy Side Effects: Common adverse effects include hair loss (alopecia) and gastrointestinal symptoms such as nausea and diarrhea25 6.
• Surgical Complications: Infection, fibrosis (scarring), stenosis (narrowing), and fistula formation may occur after surgery25 6.
• Fecal Incontinence: Loss of bowel control can result from treatment affecting the anal sphincter muscles26 .

“Most anal cancers are curable with chemoradiation, but the biggest factor affecting life expectancy is the cancer stage at diagnosis.”3

Living With Anal Cancer

Living with anal cancer involves managing both physical and emotional challenges. Patients often experience psychological distress but can find hope in effective treatments and supportive care27 28. Quality of life may be affected by treatment side effects such as pain, fatigue, and changes in bowel habits29 30.

Support systems, including counseling and patient support groups, help patients cope with the disease and its impact27 28. Active involvement in care and holistic approaches improve outcomes and well-being27 28.

💡 Did You Know? Anal cancer is an uncommon type of cancer that develops inside the lining of your anal canal or around your anus. Usually, it’s linked to an infection with high-risk strains of the HPV virus32 .

Anal Cancer FAQs

What is the difference between anal cancer and anal dysplasia?
Anal dysplasia refers to abnormal cells in the anus that are not yet cancerous but may develop into cancer over time. It is considered a precancerous condition and requires monitoring or treatment to prevent progression19 .

How does anal cancer differ from rectal or colon cancer?
Although the anus, rectum, and colon are parts of the digestive system, they are made up of different cell types. This leads to differences in cancer behavior and treatment approaches31 .

What are the survival rates for anal cancer?
The five-year relative survival rate for localized anal cancer is about 85%, decreasing to around 70% for regional spread and 36% for distant metastases2 1.

When should I see a healthcare provider?
If you experience unexplained rectal bleeding, anal pain, or other persistent symptoms, consult a healthcare professional promptly. Early diagnosis improves treatment success19 21.