Anal cancer is a rare malignancy that develops in the anus, which is the opening where solid waste (faeces or stool) exits the body. It is found at the end of the lower gastrointestinal tract (GI tract).
The lower GI tract is divided into three separate areas: the small bowel, the large bowel and the anus. The small bowel receives food from the stomach and absorbs the nutrients from the food, and is comprised of three separate parts (the duodenum, jejunum and ileum). The food is then passed onto the large bowel, where water and salts are absorbed. The large bowel also consists of three parts (the caecum, colon and rectum). What is left over is turned into solid waste (faeces or stool), and is sent to the anus to be removed from the body.
The anus is made up of two distinct regions: the anal canal, and the anal margin. The anal canal is the 4cm portion at the end of the large bowel that leads to the anal opening. This region is surrounded by two ring-shaped sphincter muscles, which are responsible for controlling the release of faeces from the body. The anal margin is the skin that internally surrounds the anal opening, and lies between the anal canal and the perianal skin (which is the skin surrounding the outside of the anal opening).
Anal cancer is slightly more common in women, and tends to be diagnosed in people over 50 years of age. However, anyone can develop this disease.
Types of Anal Cancer
There are different types of anal cancer, which are categorized based on the types of cells the cancer develops from.
Squamous Cell Carcinoma (SCC)
Anal squamous cell carcinomas are the most common type of anal cancer, and develop from the squamous cells that line the anal canal or anal margin. This type of cancer can be aggressive and can metastasise, however, it can have a good prognosis when caught early.
Adenocarcinoma
Anal adenocarcinomas are a less common subtype of anal cancer, and develop from mucus producing cells in the anal canal. These types of anal cancers are often treated similarly to bowel cancers. Anal adenocarcinomas can often be aggressive, and may not have as good of a prognosis as other types of anal cancer.
Rare forms of Anal Cancer
These types of anal cancers are very rare:
- Basal cell carcinoma (skin cancer that develops from basal cells in the perianal skin).
- Melanoma (skin cancer that develops from melanocytes in the perianal skin).
- Gastrointestinal stromal tumours (a type of sarcoma that develops from the lining of the gastrointestinal tract).
- Anal lymphoma (a very rare cancer often appearing as a type of non-Hodgkin lymphoma).
Treatment
If anal cancer is detected, it will be staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body) and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you.
Cancers can be staged using the TNM staging system:
- T (tumour) indicates the size and depth of the tumour.
- N (nodes) indicates whether the cancer has spread to nearby lymph nodes.
- M (metastasis) indicates whether the cancer has spread to other parts of the body.
This system can also be used in combination with a numerical value, from stage 0-IV:
- Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue.
- Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
- Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer.
- Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer.
- Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advanced or metastatic cancer.
Cancers can also be graded based on the rate of growth and how likely they are to spread:
- Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour.
- Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour.
- Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour.
Once your tumours have been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.
Treatment is dependent on several factors, including location, age, stage of disease and overall health.
Treatment options for anal cancers may include:
- Radiation therapy.
- Chemotherapy.
- Surgery, potentially including:
- Local excision (removal of tumour and a healthy margin of tissue surrounding it).
- Abdominoperineal resection or excision (APR or APE) (removal of the sigmoid colon, rectum and anus).
- Clinical trials.
- Palliative care.
For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.
Risk factors
While the cause of anal cancer remains unknown, the following factors may increase the likelihood of developing this disease:
- Having been infected with the human papillomavirus (HPV).
- Having a weakened immune system, potentially due to:
- Having the human immunodeficiency virus (HIV).
- Having recently had an organ transplant.
- Having an autoimmune disease, such as coeliac disease, lupus, or Grave’s disease.
- Having unprotected anal sex.
- Having multiple sexual partners.
- Having anal or genital warts.
- Having a personal history of vulvar, vaginal and/or cervical cancer.
- Having a history of smoking.
Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.
Early symptoms
In the early stages of disease, people with anal cancer may appear asymptomatic. As the cancer progresses, some of the following symptoms may appear:
- Anal/rectal bleeding.
- Blood in stool or on toilet paper.
- Bowel changes, such as difficulty controlling bowel movements.
- Mucousal discharge from the anus.
- Pain, itching, pressure, and/or discomfort around the anus.
- A lump near the anus.
- Ulcers around the anus.
- Feeling of fullness, discomfort, and/or pain in the rectum.
Not everyone with the symptoms above will have cancer but see your general practitioner (GP) if you are concerned.
Diagnosis/diagnosing
If your doctor suspects you have anal cancer, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment.
Physical Examination
Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they may examine your body to check for any abnormalities.
Digital Rectal Examination (DRE)
A digital rectal examination (DRE), also known as a digital anorectal examination, is an exam conducted by a urologist (a doctor specialising in issues pertaining to the kidneys, bladder, prostate, and male reproductive system). In this exam, the doctor will insert a finger (or ‘digit’) into your anus to feel for any lumps. If the doctor finds any abnormalities, further testing may be required.
Proctoscopy
A proctoscopy is a procedure that examines the rectum and the anus. A long, thin tube, with a light and a camera attached (a proctoscope) is inserted through the anus and rectum to determine if there are any abnormalities. This can be done under a local or general anaesthetic, and is often performed as a day procedure.
Imaging & blood tests
The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and look for signs of metastasis. Additionally, a blood and urine test may also be taken to assess your overall health and help guide treatment decisions.
Endoscopy & biopsy
An endoscopy is a surgical procedure that involves inserting a long, flexible tube with a light and small camera (endoscope) into the anal canal to observe any abnormalities. You will be given a sedative or anaesthetic throughout the procedure. You will be asked to fast for several hours prior to the procedure. An endoscopy is often done as a day surgery. Your doctor will discuss the risks and any possible complications of this procedure prior to the procedure.
Throughout the procedure, your doctor may also perform an endoscopic ultrasound to guide the needle during a biopsy, or to check for signs of cancer metastasis.
If any abnormalities are observed, your doctor will remove a small tissue sample for analysis.
Prognosis (Certain factors affect the prognosis and treatment options)
While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on the rate and depth of tumour growth, susceptibility to treatment, age, overall fitness, and medical history. Generally, early-stage anal cancers have a better prognosis and survival rates. However, if the cancer is advanced and has spread, the prognosis may not be as good and there may be a higher risk of cancer recurrence. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.
References
Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.