- Anal carcinoma is relatively uncommon tumour
- The incidence appears to be increasing
- There are 250 - 300 cases per year in England and Wales
- They account for 4% of anorectal malignancies
Pathology
- 80% are squamous cell carcinomas
- Other tumour types include melanoma, lymphoma and adenocarcinoma
- Tumour behaviour depends on its anatomical site
- Anal margin tumours are usually well differentiated, keratinising lesions
- They are more common in men and have a good prognosis
- Anal canal tumours arise above the dentate line
- They are usually poorly differentiated and non-keratinising lesions
- They are more common in women and have a worse prognosis
- Tumours above the dentate line spread to the pelvic lymph nodes
- Tumours below the dentate line spread to the inguinal nodes
Aetiology
- Anal carcinoma is more common in homosexuals
- It is also increasingly seen in those with genital warts
- Patients with genital warts often develop intraepithelial neoplasia
- Intraepithelial neoplasia appears to be premalignant
- The natural history of this premalignant state is however unknown
- Human papilloma virus (types 16,18,31 and 33) is an important aetiological factor
- 50% of tumours contain viral DNA
Clinical features
- 75% of tumours are initially misdiagnosed as benign lesions
- 50% present with perianal pain and bleeding
- Only 25% patients have identified a palpable lesion
Picture supplied by Mr N P J Cripps, Consultant Colorectal Surgeon, Chichester, United Kingdom
- 70% of patients have sphincter involvement at presentation
- This can cause faecal incontinence
- Neglected tumours can cause a rectovaginal fistula
- Only 50% of patients with palpable inguinal nodes have metastatic disease
Investigation
- Rectal EUA and biopsy is the most useful 'staging' investigation
- Endoanal ultrasound is often impossible due to pain
- CT or MRI can be used to assess pelvic spread
Management
- The management of anal carcinoma has changed over the last 15 years
- Was considered a 'surgical' disease requiring radical abdominoperineal resection
- Now most patients are managed with radiotherapy
- The role of chemotherapy is currently undergoing investigation
- Radiotherapy is given to tumour and inguinal nodes
- 50% of patients respond to treatment
- Over 5 year survival is 50%
- Surgery is required for:
- Tumours that fail to respond to radiotherapy
- Large tumours causing gastrointestinal obstruction
- Small anal margin tumours without sphincter involvement
Bibliography
Frische M, Melbye M. Trends
in the incidence of anal carcinoma in Denmark. Br Med J 1993;
306: 419-422.
Schofield J, Hickson W, Smith
J et al. Anal intraepithelial neoplasia:
part of a multifocal disease process. Lancet 1992;
340: 1271-1273. |