Anal cancer is an uncommon malignancy that originates in the tissues of the anus, the opening at the end of the gastrointestinal tract. It is distinct from colorectal cancers, affecting a different anatomical region and often requiring different diagnostic and therapeutic approaches.
WHAT IS ANAL CANCER?
The most common type of anal cancer is squamous cell carcinoma, which arises from the squamous cells lining the anal canal below the anal verge.
Less frequent type of anal cancer is adenocarcinoma, arising from glandular cells above the anal verge.
Other uncommon types include basaloid carcinoma, melanoma, lymphoma, and sarcoma. Each type has unique characteristics and may require different treatment strategies.
Symptoms of anal cancer can be subtle initially but may become more pronounced as the disease progresses. Common signs and symptoms include:
- Rectal bleeding or blood in the stool
- Pain or a feeling of pressure in the anal area
- Anal itching or discomfort
- Lumps or growths near the anus
- Changes in bowel habits, such as constipation or diarrhoea
- Unexplained weight loss
- Swollen lymph nodes in the groin or anal area
Several factors can increase the risk of developing anal cancer, including:
- Human Papillomavirus (HPV) infection: A major risk factor, especially for squamous cell carcinoma.
- Anal intercourse: Increases the risk of HPV transmission and subsequent cancer development.
- Smoking: Linked to an increased risk of anal cancer.
- Immunosuppression: Individuals with weakened immune systems, such as those with HIV/AIDS or on immunosuppressive therapy, have a higher risk.
- Age: The incidence of anal cancer increases with age.
- History of cervical, vaginal, or vulvar cancer: Indicates potential HPV-related pathology.
Types of Anal Cancer
The most common type of anal cancer is squamous cell carcinoma, which arises from the squamous cells lining the anal canal below the anal verge.
Less frequent type of anal cancer is adenocarcinoma, arising from glandular cells above the anal verge.
Other uncommon types include basaloid carcinoma, melanoma, lymphoma, and sarcoma. Each type has unique characteristics and may require different treatment strategies.
Signs and Symptoms
Symptoms of anal cancer can be subtle initially but may become more pronounced as the disease progresses. Common signs and symptoms include:
- Rectal bleeding or blood in the stool
- Pain or a feeling of pressure in the anal area
- Anal itching or discomfort
- Lumps or growths near the anus
- Changes in bowel habits, such as constipation or diarrhoea
- Unexplained weight loss
- Swollen lymph nodes in the groin or anal area
Risk Factors
Several factors can increase the risk of developing anal cancer, including:
- Human Papillomavirus (HPV) infection: A major risk factor, especially for squamous cell carcinoma.
- Anal intercourse: Increases the risk of HPV transmission and subsequent cancer development.
- Smoking: Linked to an increased risk of anal cancer.
- Immunosuppression: Individuals with weakened immune systems, such as those with HIV/AIDS or on immunosuppressive therapy, have a higher risk.
- Age: The incidence of anal cancer increases with age.
- History of cervical, vaginal, or vulvar cancer: Indicates potential HPV-related pathology.
Diagnosis
Diagnosing anal cancer involves several steps:
Physical Examination
Includes a digital rectal examination (DRE) and inspection of the anal area.
Anoscopy
A procedure using a small scope to examine the anal canal and rectum.
Biopsy
A tissue sample is taken for histopathological analysis to confirm the presence and type of cancer.
Imaging Studies
Techniques such as trans-anal ultrasound, MRI, CT scans, and PET scans are used to determine the extent and spread of the cancer.
Treatment
Treatment for anal cancer depends on various factors, including the type, size, location, and stage of the tumour, as well as the patient’s overall health. Common treatment options include:
Chemoradiation
The standard treatment for squamous cell carcinoma, combining chemotherapy and radiation to shrink the tumour and destroy cancer cells.
Supportive Care
Includes pain management, nutritional support, and psychological support to improve quality of life, especially in advanced stages.
Surgery
Used for specific cases, such as when the cancer does not respond to chemoradiation or if it recurs. Procedures range from local excision to more extensive surgeries like abdominoperineal resection (APR) for advanced cases.
Immunotherapy and Targeted Therapy
Emerging treatments, particularly for advanced or metastatic cases. Immunotherapy helps the immune system target cancer cells, while targeted therapy focuses on specific molecular abnormalities in the cancer.
Radiotherapy
Different types of radiotherapy can be employed depending on the specific characteristics of the tumour, its location, and the overall treatment plan. Here are the main types of radiotherapy used in the treatment of anal cancer:
a. External Beam Radiation Therapy (EBRT)
External Beam Radiation Therapy (EBRT) is the most common form of radiotherapy used for anal cancer. In this technique, high-energy x-rays or other types of radiation are directed at the cancerous area from outside the body.
- Three-Dimensional Conformal Radiation Therapy (3D-CRT): This technique uses imaging technology to map the exact shape and size of the tumour, allowing the radiation beams to be shaped precisely to the contours of the tumour. This minimises exposure to surrounding healthy tissues.
- Intensity-Modulated Radiation Therapy (IMRT): A more advanced form of EBRT, IMRT allows the intensity of the radiation beams to be adjusted. It delivers higher doses to the tumour while minimising exposure to surrounding normal tissues, potentially reducing side effects.
- Volumetric Modulated Arc Therapy (VMAT): A type of IMRT that delivers radiation in a single or multiple arcs around the patient. This approach can provide highly conformal treatment with a shorter delivery time.
b. Internal Radiation Therapy (Brachytherapy)
Brachytherapy involves placing a radioactive source directly into or near the tumour. However, brachytherapy is less commonly used for anal cancer compared to other cancers like cervical or prostate cancer.
c. Proton Beam Therapy
Proton Beam Therapy is an advanced form of radiotherapy that uses protons instead of x-rays. Proton beam therapy is especially beneficial for tumours located near critical structures, but its availability is limited and may not be widely used for anal cancer.
d. Stereotactic Body Radiation Therapy (SBRT)
Stereotactic Body Radiation Therapy (SBRT), also known as stereotactic ablative radiotherapy (SABR), delivers very high doses of radiation with extreme precision over a few sessions. While SBRT is more commonly used for small, well-defined tumours in other parts of the body, its role in anal cancer is limited and typically reserved for certain cases, such as recurrent disease or metastases.
e. Combination with Chemotherapy
In most cases, radiotherapy for anal cancer is combined with chemotherapy (chemoradiation), which enhances the sensitivity of cancer cells to radiation and increases the effectiveness of the treatment. The choice of radiotherapy technique depends on various factors, including the tumour’s size, location, stage, and the patient’s overall health. The treatment plan is tailored to each patient’s needs, aiming to maximise tumour control while minimising side effects.
f. Total Skin Electron Beam Therapy (TSEBT)
Prevention
Prevention strategies for anal cancer focus on reducing risk factors and promoting early detection:
- HPV Vaccination: Effective in preventing HPV-related cancers, including anal cancer. The vaccine is recommended for both males and females, ideally before becoming sexually active.
- Safe Sexual Practices: Using condoms and limiting the number of sexual partners can reduce the risk of HPV infection.
- Regular Screening: Especially for high-risk individuals, such as those with a history of HPV infection, HIV, or immunosuppression.
- Smoking Cessation: Quitting smoking reduces the risk of developing anal and other cancers.
Early detection and awareness of risk factors are crucial in managing and preventing anal cancer, improving outcomes and quality of life for affected individuals.
