Introduction

Anal cancer, like carcinoma of the cervix, is strongly associated with human papilloma virus (HPV) infection. In the past few decades, treatment has swung away dramatically from primary surgery to definitive chemoradiotherapy, with the evident physical and psychosocial benefits of organ preservation. Tumours of lower stage T1 or T2, N0, have an excellent outcome with the chemoradiotherapy approach. Unfortunately, many patients present with T3, T4 or N ≥ 1 disease and they have a significant risk of both locoregional and subsequent distant failure. Half of patients still die within 5 years of treatment. Therefore, efforts are ongoing to improve outcomes via better local and systemic therapy.

Types of anal tumour

Types of anal tumour are shown in Table 14.1.

Anatomy

The anal canal extends from the rectum to the junction of the hair-bearing skin of the perianal region. It is 3 to 4 cm long and its walls are kept in apposition by the sphincter muscles, except during defaecation. The anal margin is the perianal skin immediately adjacent to the distal limit of the anal canal. The anal verge is the lower end of the anal canal.

The tumours can be divided into three types:

1. Anal-margin tumours are usually small and well differentiated and are more common in men.

2. Anal-canal tumours are more common than those at the anal margin. They are more common in women (male-to-female ratio ∼1:2.5), are often moderately or poorly differentiated, and carry a worse prognosis.

3. Dual-component tumours have both anal-margin and -canal components and it is not possible to define from where the tumour originated. These comprise the majority of tumours.