There is wide geographical variation in the incidence of anal cancers around the world. Areas of high incidence include Recife in Brazil and the Philippines. Interestingly, those areas with a high incidence of anal cancer also tend to have a high incidence of cervical, vulval, and penile tumours.
Epidemiological evidence has suggested that anal cancer may be associated with anal sexual activity. Male homosexual activity and HIV infection are strongly associated with the incidence of anal squa-mous carcinoma. Most specifically, human papillomavirus has been shown to be an important aetiological factor in anal, cervical, vulval, and penile squamous tumours.
♦ Ano-genital papillomavirus lesion —condylomata
—intra-epithelial neoplasia —invasive carcinoma
♦ Colposcopy useful
♦ High-grade and intra-epithelial lesions (AIN 111) —pigmented or white
—flat or raised
—if ulcerated, may be invasive
♦ Biopsy is essential
Included within the category of epidermoid tumours are:
♦ Squamous cell
♦ Basaloid (or cloacogenic) carcinomas
♦ Mucoepidermoid cancers
Anal canal cancer spreads locally. The anal sphincters and the recto-vaginal septum, perineal body, and the vagina (in more advanced cases) are common sites of spread. Lymph node spread occurs initially to the perirectal group of nodes and thereafter to inguinal, haemor-rhoidal, and lateral pelvic lymph nodes. Approximately 10% of patients will present with inguinal lymph node involvement, but this rises to approximately 30% when the primary tumour is greater than 5 cm in diameter. Synchronously involved nodes carry a poorer prognosis than metachronous nodal involvement.
Blood-borne spread tends to occur late and is usually associated with advanced local disease. The most common sites of metastases are the liver, lung, and bones.
Clinical presentation and staging
♦ Symptoms of epidermoid anal cancer —pain
—faecal incontinence —ano-vaginal fistula Cancer of the anal margin often has the appearance of a malignant ulcer, with a raised, everted, indurated edge. Lesions within the canal may not be visible, although they may spread to the anal verge. Digital examination of the anal canal is usually painful and the canal often feels indurated and distorted. It is often difficult to distinguish an anal cancer from a low rectal tumour.
Approximately one-third of patients with anal carcinoma have enlarged inguinal lymph nodes on presentation, but less than half this number have metastatic nodes. Often the nodes are secondarily infected or reactive. Biopsy or fine-needle aspiration is therefore necessary to confirm involvement of the groin nodes if radical block dissection is contemplated.
The most widely used staging system is that of the UICC (Union International Contré Cancer).
Examination under anaesthesia is the mainstay in the diagnosis and investigation of this tumour. Ultrasound scanning, CT, and magnetic resonance scanning may provide additional information.
Until 10 years ago the standard treatment for anal canal tumours was abdominoperineal resection, while anal margin growths were viewed as equivalent to skin tumours elsewhere and treated by local excision. Over the past few years, radiotherapy and/or chemotherapy have become increasingly popular and in many cases are the treatment of choice.
Compared to anal margin cancer, anal canal cancer is more likely to be locally advanced and to be associated with subsequent metastases, perhaps explaining the general preference for radical surgery. Around 20% are incurable surgically at presentation. Most recurrence occurs loco-regionally.
Non-surgical treatment (chemo-irradiation) for anal cancer has become increasingly popular after pioneering work in the US by Norman Nigro. The drugs used are usually 5FU and mitomycin C.
This particular combination of chemotherapy was developed empirically as a pre-operative regimen aimed at improving the results of radical surgery1. The radiotherapy consists of 30 Gy of external-beam irradiation over a period of three weeks.
Chemo-irradiation was shown to be superior to radiotherapy alone in a recent British trial2.
Small lesions at the anal margin may still best be treated by local excision alone, obviating the need for protracted courses of non-surgical therapy.
An important role for the surgeon is in treatment after failure of primary non-surgical therapy, either early or late. The appearance of the primary site can be misleading after radiotherapy. A proportion of patients develop complications such as radio-necrosis, fistula, or incontinence, following radical radiation or combined therapy.
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