anal squamous cell carcinoma
Wednesday 1 May 2013
anal epidermoid carcinoma
80% of anal malignant tumors are squamous cell carcinomas (SCCs).
Anal cancer is an uncommon malignancy, accounting for only about 4% of all cancers of the lower alimentary tract.
The annual incidence is about 1 in 100,000. The incidence is higher in women and is increasing.
Anal canal tumours are usually poorly differentiated. They are more common in women and have a worse prognosis.
Systemic spread of anal cancer occurs in fewer than 10% of cases. The most common sites of spread are to the liver and lungs.
Human papillomavirus (HPV) is an important aetiological factor and 50% of tumours contain viral DNA. Anal intercourse and a high lifetime number of sexual partners increase the risk of HPV infection. Anal carcinoma is more common in homosexuals.
It is increased in HIV infection and in patients taking immunosuppressive drugs for HIV infection. It is twice as common in HIV-positive as it is in HIV-negative homosexual men.
Other important risk factors include immune suppression in transplant recipients and cigarette smoking.
Previous malignancy (gynaecological, lymphoma or leukaemia) or subsequent malignancy (eg lung, bladder, vulva, vagina or breast) is more likely in patients with anal cancer.
Anal margin tumours
Anal margin tumours are usually well differentiated. They are more common in men and have a good prognosis.
- Presentation includes perianal pain and bleeding, a palpable lesion and faecal incontinence.
- Neglected tumours in women can cause a rectovaginal fistula.
- Tumours near the anal margin spread to the inguinal lymph nodes; those higher in the anal canal spread to the pelvic lymph nodes.
- Suspicious lesions should always be biopsied.
- Rectal examination under anaesthesia and biopsy are the most useful staging investigations.
- Imaging modalities used for staging include CT, MRI, endo-anal ultrasound and positron emission tomography (PET).
- Patients should be tested for relevant infections, including HIV, and other possible malignancies.
The following is a staging system for anal canal cancer that has been described by the American Joint Committee on Cancer and the International Union Against Cancer.
Tumours of the anal margin (below the anal verge and involving the perianal hair-bearing skin) are classified with skin tumours.
Primary tumour (T):
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).
Regional lymph nodes (N):
NX: regional lymph nodes cannot be assessed.
N0: no regional lymph node metastasis.
N1: metastasis in perirectal lymph node(s).
N2: metastasis in unilateral internal iliac and/or inguinal lymph node(s).
N3: metastasis in perirectal and inguinal lymph nodes and/or bilateral internal iliac and/or inguinal lymph nodes.
Distant metastasis (M):
MX: distant metastasis cannot be assessed.
M0: no distant metastasis.
M1: distant metastasis.
Stage 0: Tis, N0, M0.
Stage I: T1, N0, M0.
Stage II: T2, N0, M0; T3, N0, M0.
Stage IIIA: T1, N1, M0; T2, N1, M0; T3, N1, M0; T4, N0, M0.
Stage IIIB: T4, N1, M0; any T, N2, M0; any T, N3, M0.
Stage IV: any T, any N, M1.