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.
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
The following is a T stage system for anal cancer described by the American Joint Committee on Cancer and the International Union Against Cancer:
- 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:
| TX | primary tumour cannot be assessed |
| T0 | no evidence of primary tumour |
| Tis | carcinoma in situ |
| T1 | tumour 2 cm or less in greatest dimension |
| T2 | tumour more than 2 cm but not more than 5 cm in greatest dimension |
| T3 | tumour more than 5 cm in greatest dimension |
| T4 | tumour 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) |