Overview
Anal cancer is a type of cancer where the malignant cells form in the tissues of the anus, which is the end of the gastrointestinal tract and is comprised of the last inch or so of the large intestine. This type of cancer is relatively rare when compared to other forms of digestive system cancers such as colorectal cancer.
Type of cancer
Anal cancer is primarily categorized by the type of cells that become malignant. The main types of anal cancer include:
 
Squamous Cell Carcinoma: This is the most common type of anal cancer, originating in the squamous cells that line the majority of the anal canal.
Adenocarcinoma: This type of cancer begins in the glandular cells of the anus that produce mucus. It is less common than squamous cell carcinoma.
Melanoma: Though it is more well-known for affecting the skin, melanoma can also begin in the skin-like cells of the anal region.
Basal Cell Carcinoma: This is a type of skin cancer that can sometimes occur on the skin around the anus.
Sarcoma: These are rare types of cancer that start in the muscle, fat, connective tissue, and other supporting tissues of the anal area.
The treatment protocol may vary depending on the type of anal cancer, with squamous cell carcinoma being the most studied and having more defined treatment options.
 
Stage
Anal cancer staging is typically defined according to the American Joint Committee on Cancer (AJCC) TNM system, which considers three key factors:
1. Tumor (T): Size and depth of the primary tumor.
2. Node (N): Lymph node involvement.
3. Metastasis (M): Spread of cancer to other parts of the body.
Based on these factors, anal cancer is staged as follows:
Stage 0 (Carcinoma in Situ):
· Tis, N0, M0: Abnormal cells are found only in the first layer of cells lining the anus and have not spread deeper.
Stage I:
· T1, N0, M0: The tumor is 2 cm or smaller and has not spread to nearby lymph nodes or distant sites.
Stage II:
· Divided into IIA and IIB:
o Stage IIA (T2-3, N0, M0): The tumor is more than 2 cm but not larger than 5 cm (T2), or the tumor is larger than 5 cm (T3), with no lymph node involvement or distant metastasis.
o Stage IIB (T1-2, N1, M0): The tumor is 2 cm or smaller (T1), or more than 2 cm but not larger than 5 cm (T2), and it has spread to nearby lymph nodes (N1), but no distant metastasis.
Stage III:
· Divided into IIIA, IIIB, and IIIC, depending on the size of the tumor, lymph node involvement, but no distant metastasis:
o Stage IIIA (T3, N1, M0 or T1-3, N2, M0): The tumor is any size and has spread to lymph nodes near the rectum (N2), or the tumor is larger than 5 cm and has spread to the first group of nearby lymph nodes (N1).
o Stage IIIB (T4, N0-2, M0): The tumor is any size and may be attached to nearby organs or structures (T4), and it might or might not have spread to nearby lymph nodes.
o Stage IIIC (Any T, N3, M0): The tumor is any size and has spread to lymph nodes near the aorta (N3), which are not near other pelvic organs.
Stage IV:
· Divided into IVA and IVB:
o Stage IVA (Any T, any N, M1a): The cancer has spread to nearby organs or the perineum (M1a) and may have spread to any lymph node.
o Stage IVB (Any T, any N, M1b): The cancer has spread to distant parts of the body beyond the pelvis (M1b), such as to the liver, lungs, or non-regional lymph nodes.
Staging is critical as it directs the treatment approach and provides information regarding the prognosis. Treatment options can include surgery, chemotherapy, radiation therapy, or combinations of these modalities. The stage-specific treatment strategies aim to manage the disease effectively while preserving the anal sphincter function whenever possible.
 
 
Incidence Rates
Anal cancer incidence rates vary significantly across the globe and within Asia. Here’s a summary of the key points:
· The global age-standardized incidence rate (ASR) of anal cancer was 0.6 per 100,000 persons in 2020.
· The ASR was higher in high-income countries (0.9 per 100,000) than in low- and middle-income countries (0.4 per 100,000).
· The ASR was higher in females (0.7 per 100,000) than in males (0.5 per 100,000).
· The ASR of anal cancer has been increasing in many countries, including the United States, Australia, the United Kingdom, France, Germany, Italy, Spain, Japan, China, India, Thailand, South Korea, Singapore, Malaysia, and Indonesia.
· The increase in anal cancer incidence is not fully understood, but potential factors include human papillomavirus (HPV) infection, smoking, immunosuppression, and sexual behavior.
· Prevention and early detection of anal cancer are crucial to reduce the associated mortality and morbidity.
For the most current and region-specific data, local cancer registries or studies published in medical journals would provide the most accurate information. Multinational organizations like the World Health Organization (WHO) and networks such as GLOBOCAN also offer estimates on cancer incidence, which include Asian countries in their datasets.
 
Symptoms
Anal cancer can cause various symptoms, such as:
· Blood in the stool or rectal bleeding
· A change in bowel habits, such as diarrhea, constipation, or narrowing of the stool
· Abdominal pain, cramps, bloating, or gas
· Unexplained weight loss
· Weakness, fatigue, or anemia
· A feeling that the bowel is not empty after a bowel movement
· Itching in or around the rectum
· A lump or mass at the anal opening
· Unusual discharge from the anus
· Incontinence of stool (loss of bowel control)
· Swollen lymph nodes in the anal or groin areas
These symptoms are not always obvious and can be caused by other conditions, such as hemorrhoids, infections, or inflammatory bowel disease. Therefore, it is important to consult a doctor if any of these symptoms persist for more than a few weeks.
 
Cause
The exact cause of anal cancer is not known, but it is thought to involve changes in the DNA of the cells that line the anus. These changes can cause the cells to grow abnormally and form tumors. Some of these changes may be inherited, while others may be influenced by environmental or lifestyle factors. Anal cancer can develop from abnormal growths called polyps that form on the lining of the colon or rectum. Polyps are usually benign (non-cancerous), but some can become malignant (cancerous) over time. Detecting and removing polyps can prevent anal cancer. The most common type of anal cancer is adenocarcinoma, which starts in the cells that make mucus and other fluids.
Anal cancer is closely related to a sexually transmitted infection called human papillomavirus (HPV), which is prevalent in a majority of anal cancer cases. HPV is thought to be the most common cause of anal cancer. HPV infection can also cause genital warts and cervical cancer.
Risk factors
Other factors that may increase the risk of anal cancer include:
· Older age: Anal cancer is more common in people who are over 50 years old, but it can also affect younger people. The numbers of people younger than 50 who have anal cancer has been growing. Doctors don’t know why.
· Race: Black people in the United States have a higher risk of anal cancer than people of other races.
· A personal or family history of colorectal cancer or polyps: Having a close relative, such as a parent, sibling, or child, who has had colorectal cancer or polyps can increase the risk of anal cancer.
· Genetic mutations: Some inherited gene mutations, such as Lynch syndrome or familial adenomatous polyposis (FAP), can increase the risk of anal cancer, as well as other cancers. People with these mutations can get tested and take preventive measures, such as regular screening or surgery.
· Lifestyle factors: Smoking, drinking alcohol, eating a diet high in red or processed meat and low in fiber, being overweight or obese, and being physically inactive can increase the risk of anal cancer.
· Medical conditions: Having chronic inflammation of the colon or rectum, such as ulcerative colitis or Crohn’s disease, can increase the risk of anal cancer. Having type 2 diabetes or certain infections, such as human papillomavirus (HPV) or Helicobacter pylori, may also increase the risk of anal cancer.
 
Diagnosis and Test
The diagnosis of anal cancer involves several procedures and tests, including:
Digital Rectal Examination (DRE): This is a manual inspection by a healthcare provider to feel for abnormalities.
Anoscopy: This procedure uses a small scope to view the inside of the anus and rectum.
Biopsy: This involves collecting tissue samples from suspicious areas for microscopic examination to confirm malignancy.
Fine Needle Aspiration (FNA) Biopsy: This procedure uses a thin needle to extract cells from a tumor.
Excisional Biopsy: This involves the complete removal of a suspicious lesion, which is then examined under a microscope.
Human Papillomavirus (HPV) Testing: Since many anal cancers are associated with HPV, tests can determine the presence of high-risk HPV types.
Imaging Tests:
· Ultrasound: This may be used to examine suspicious areas.
· Computed Tomography (CT) Scan: This is used to determine the spread within the pelvis and to distant areas.
· Magnetic Resonance Imaging (MRI): This provides detailed images of the anal area and is useful in surgical planning.
· Positron Emission Tomography (PET) Scan: Often combined with a CT scan (PET-CT), this is used to check for the spread of cancer.
Blood Tests: While not specific for diagnosing anal cancer, they can indicate the overall health status of the patient and can include full blood count, kidney and liver function tests, and tumor markers.
High-resolution Anoscopy (HRA): Similar to a cervical colposcopy, HRA uses a high-powered scope to look for areas of abnormal cells to biopsy, often used in patients with abnormal anal cytology results.
 
Treatment
Treatment of anal cancer often involves a combination of chemotherapy and radiation therapy (chemoradiotherapy), with surgery primarily reserved for cases that do not respond or recur.
Chemoradiotherapy: The concurrent use of radiation therapy and chemotherapy is the standard initial treatment for most anal cancers.
Chemotherapy: Drugs like fluorouracil (5-FU) or capecitabine and mitomycin are commonly used to enhance the effectiveness of radiation therapy.
Radiation Therapy: This target cancerous cells in the anal area and may cause side effects such as skin irritation or fatigue.
Surgery:
· Local Resection: This is for smaller, early-stage tumors located in the anal margin.
· Abdominoperineal Resection (APR): This is for more extensive cancers or those not responding to chemoradiotherapy. It involves removing the anus, rectum, and part of the sigmoid colon.
Immunotherapy: This may be an option for some metastatic or advanced anal cancers not responding to standard treatments, particularly for patients with evidence of high microsatellite instability (MSI-H) or mismatch repair deficiency (dMMR).
Targeted Therapy: This is for certain advanced cases, where the cancer has specific genetic features making it suitable for targeted drug treatments.
Follow-Up and Monitoring: Regular check-ups post-treatment are necessary to monitor for recurrence or manage treatment side effects.
HPV Vaccination: This is recommended to prevent HPV infections, which can reduce the risk of anal cancer. It is a preventative strategy, not a treatment.
 
 
 
Prognosis
The prognosis of anal cancer depends on several factors:
· Stage of Cancer: Earlier detection and treatment generally lead to a better prognosis.
· Type of Cancer: The most common type is squamous cell carcinoma. Rarer types like adenocarcinoma, melanoma, and neuroendocrine tumors usually have a worse prognosis.
· Survival Rate: The 5-year relative survival rate for all types of anal cancer is 69%. However, this varies depending on the stage of the cancer.
· Treatment Response: The prognosis can change over time, depending on how the cancer responds to treatment and whether it recurs or spreads.
It’s important to discuss your specific prognosis with your healthcare provider.
Supportive
Caring for a patient with anal cancer involves several key aspects:
1. Emotional Support: Offering encouragement and a listening ear can be invaluable.
2. Medical Assistance: Assisting with medications and managing symptoms and side effects.
3. Practical Help: Helping with medical appointments, providing transportation, assisting with meals, and helping with household chores.
4. Communication: Facilitating communication with the healthcare team.
5. Treatment Adherence: Ensuring the patient adheres to the treatment plan, which often combines chemotherapy and radiation therapy.
6. Monitoring: Keeping an eye on the patient’s condition and reporting any changes or concerns to the healthcare team.
Remember, each patient’s needs are unique, and the care approach should be tailored to their specific situation. It’s also crucial for caregivers to take care of their own physical and emotional health. If needed, seek support from healthcare professionals or support groups. They can provide valuable resources and advice.