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ALL / Gastroenterology

Anal cancer

Anal cancer

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). 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.

Epidemiology
  • Anal cancer is relatively rare, with an annual incidence in the UK of about 1.5 in 100,000. However, its incidence is rising, especially amongst men who have sex with men, due to widespread infection by human papillomavirus (HPV).2
  • 1:2 male:female ratio.3
  • The average age of presentation in the UK is 85-89 years.
  • 30-40% of patients present with lymph node involvement at diagnosis, however, distant spread is uncommon, with 5-8% of cases presenting with extrapelvic metastases at time of diagnosis.1

Risk factors
  • HPV infection causes 80-85% of SSCs of the anus (especially HPV16 subtype)
  • 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.

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.

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.

T 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)
+PassMedicine Notes

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). 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.

Epidemiology
  • Anal cancer is relatively rare, with an annual incidence in the UK of about 1.5 in 100,000. However, its incidence is rising, especially amongst men who have sex with men, due to widespread infection by human papillomavirus (HPV).2
  • 1:2 male:female ratio.3
  • The average age of presentation in the UK is 85-89 years.
  • 30-40% of patients present with lymph node involvement at diagnosis, however, distant spread is uncommon, with 5-8% of cases presenting with extrapelvic metastases at time of diagnosis.1
Risk factors
  • HPV infection causes 80-85% of SSCs of the anus (especially HPV16 subtype)
  • 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.
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.
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.
T 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) |

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