Anal cancer is a relatively uncommon, accounting for less than 2% of large bowel malignancies, and most of the cases are made of squamous cell carcinoma.
It accounts for less than 2% of large bowel malignancies and 1-6% of anorectal tumours (~1.5% of all gastrointestinal tract malignancies in the United States 14).
There may be a slight male predilection where its incidence has been reported to be approximately 0.5 per 100 000 in men and 1.0 per 100 000 in women 1. Its incidence is thought to be rising over the years 5.
Approximately 45% of patients may present with bleeding per rectum. Around 30% of patients may have pain and/or a sensation of a mass.
Anal carcinoma typically originates between the anorectal junction above and the anal verge below. The vast majority of anal canal cancers are squamous cell cancers. See WHO classification of anal canal tumours.
Both male and female 15:
- HPV / HIV infection
- number of lifetime sexual partners, and receptive anal intercourse
In females: previous in situ or invasive cervical, vulval or vaginal cancer 15.
- tumour above dentate line: to pararectal and paravertebral nodes 13
- tumour below dentate line: to inguinal and femoral nodes 13
Imaging performed before treatment provides an assessment of the extent of local disease and nodal involvement. Accurate delineation of the disease in relation to the rest of the perineal anatomy is of paramount importance in initial imaging assessment. The size of the tumour is also considered a critical prognostic factor (see staging of anal cancer) 13.
Endoanal ultrasound can sometimes be used in locoregional staging 6. Some authors suggest that endoanal ultrasound can accurately determine the depth of penetration of the carcinoma into the sphincter complex and can be used to accurately gauge the response of these tumours to chemoradiation therapy 8.
MRI is the modality of choice in the assessment of locoregional disease and is performed with performed with a dedicated protocol: see MRI protocol for assessment of anal cancer.
Reported typical signal characteristics include 2:
- T1: primary and recurrent tumours are usually of low to intermediate signal intensity relative to skeletal muscle
- T2: primary and recurrent tumours are generally of high signal intensity relative to skeletal muscle
Nodal metastases have a signal intensity similar to that of the primary tumour.
Recent research suggests that there are grounds for using PET-CT routinely in the workup of anal cancer, as it alters the initial staging sufficiently frequently 4.
Treatment and prognosis
Treatment is often with a combination of chemotherapy and radiotherapy (often given concurrently) and is usually curative. Approximately 50-60% are thought to present with T1 to T2 lesions carrying a 5-year survival of 80-90% 3. Some authors suggest a benefit of a salvage abdominoperineal resection (APR) for those patients with failed chemoradiation 10,12.
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