Introduction

Anal cancer is defined as a malignancy which lies exclusively in the anal canal, the borders of which are the anorectal junction and the anal margin (area of pigmented skin surrounding the anal orifice)

Epidemiology

  • Incidence: 2.50 cases per 100,000 person-years
  • Peak incidence: 60-70 years
  • Sex ratio: more common in females 2:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Risk factors
  • HPV infection causes 80-85% of SSCs of the anus (usually HPV16 or HPV18 subtypes).
  • Anal intercourse and a high lifetime number of sexual partners increases the risk of HPV infection.
  • Men who have sex with men have a higher risk of anal cancer.
  • Those with HIV and those taking immunosuppressive medication for HIV are at a greater risk of anal carcinoma.
  • Women with a history of cervical cancer or cervical intraepithelial neoplasia (CIN) are also at greater risk of anal cancer.
  • Immunosuppressive drugs used in transplant recipients increase the risk of anal cancer.
  • Smoking is also a risk factor.

Pathophysiology

80% of anal cancers are squamous cell carcinomas (SSCs). Other types include melanomas, lymphomas, and adenocarcinomas. The lymphatic drainage, and therefore, tumour spread, varies in different parts of the canal: anal margin tumours spread to the inguinal lymph nodes and those which are more proximal spread to the pelvic lymph nodes.

Clinical features

Patients typically present with a subacute onset of:
  • Perianal pain, perianal bleeding
  • A palpable lesion
  • Faecal incontinence
  • A neglected tumour in a female may present with a rectovaginal fistula.

Referral criteria

NICE cancer referral guidelines for anal cancer suggest the following:


Consider a suspected cancer pathway referral (for an appointment within 2 weeks) for anal cancer in people with an unexplained anal mass or unexplained anal ulceration.

Investigations

Investigations
  • T stage assessment: examination, including a digital rectal examination, anoscopic examination with biopsy, and palpation of the inguinal nodes
  • Imaging modalities: CT, MRI, endo-anal ultrasound and PET
  • The patient should be tested for relevant infections, including HIV

Staging

The following is a T stage system for anal cancer described by the American Joint Committee on Cancer and the International Union Against Cancer:

TXprimary tumour cannot be assessed
T0no evidence of primary tumour
Tiscarcinoma in situ
T1tumour 2 cm or less in greatest dimension
T2tumour more than 2 cm but not more than 5 cm in greatest dimension
T3tumour more than 5 cm in greatest dimension
T4tumour of any size that invades adjacent organ(s) - for example, vagina, urethra, bladder (direct invasion of the rectal wall, perirectal skin, subcutaneous tissue, or the sphincter muscle(s) - is not classified as T4)