• 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.