Section: Colorectal Sub-section: Proctology Curriculum: Curriculum, page 23
- 80% of anal cancer as squamous in origin. 10% adenocarcinomas from glandular mucosa of upper anal canal, anal glands and ducts. Rare tumours are melanoma; very rare are lymphoma and sarcoma.
- 90% caused by HPV
Epidemiology
Incidence 1/100,000, F>M. Median age 60.
Pathophysiology
- HPV 16 (84%), 18, 31 & 33. - HPV 6 & 11 cause warts & low-grade intraepithelial neoplasia but less common in cancer. - HPV for anal SCC linked to cervical, vulva and penile SCC - HIV risk factor - Smoking - Receptive anal intercourse
- Anal intraepithelial neoplasia is the pre-malignant condition
Patterns
Perianal
- Tend to be well-differentiated and keratinising Anal canal
- Often poorly differentiated and generally have a worse prognosis
Non HPV related have worse response to treatment
Spread
- Local spread cephalad and outwards.
- Lymph node mets frequent
- Upper anal canal tumours tend to spread to mesorectal/internal iliac lymph nodes
- Lower/perianal tumours to inguinal/external iliac lymph nodes
- Distant mets uncommon
Clinical
- Symptoms:
- Pain & bleeding (50%). Mass (25%), pruritis and discharge.
- Faecal incontinence, rectovaginal fistula in advanced.
- Signs:
- Malignant ulcer with raised, everted, indurated edge.
- Distortion of anal canal. Tenderness.
- Palpable perirectal and inguinal nodes
Investigations
- Examination under anaesthesia
- Can assess tumour – size, involvement of adjacent structures and nodal involvement
- Biopsy
- Need to do vaginal exam
- Colonoscopy
- MRI pelvis – all patients.
- CT CAP – all patients
- PET-CT – may be used to help plan radiotherapy and improved assessment of locoregional nodes.
- Endoanal USS – may be useful in small tumours, however more information on MRI.
- FNA – for inguinal nodes if unclear clinically and radiologically.
- Tumour markers – not useful.
- Anal Pap smear
Staging
| TNM stage | ||
|---|---|---|
| T stage | N stage | M stage |
| T1 – < 2 cm | N1 – mesorectal nodes | M0 – no metastasis |
| T2 – 2 – 5 cm | N2 – unilateral internal iliac or inguinal nodes | M1 – distant metastasis |
| T3 - > 5 cm | N3 – perirectal and inguinal lymph nodes or bilateral internal iliac and/or inguinal lymph nodes | |
| T4 – Invasion in adjacent organs (e.g. vagina, urethra) |
Management
Chemoradiotherapy
- Current standard of care is chemoradiotherapy
- 50.4 Gy radiotherapy in 28 daily fractions with Mitomycin C and 5FU (Modified Nigro protocol); except where local excision is complete or radiotherapy contraindicated.
- 90% complete response
- Equivalent survival rates to surgery, with avoidance of stoma.
- UKCCCR ACT I compared chemo-irradiation with radiotherapy alone; showed fewer deaths and reduced local failure with combination therapy.
- Complications of chemoradiation:
- Diarrhoea, mucositis, myelosuppression, skin erythema and desquamation.
- Late complications: anal stenosis and fistula formation. May defunction anterior tumours in women due to high incidence of fistula during radiotherapy.
- Long term outcomes
- Faecal and urinary incontinence (~40%)
- Sexual function (satisfied in only 24%)
Surgery
- Not main therapeutic role
- Useful for initial diagnosis – EUA + biopsy
Local excision
- T1 (< 2cm) at anal margin may be treated by local excision. Need clear margin of > 5 mm skin and deeper tissue.
- Anal canal should be biopsied only, due to risk of incontinence with local excision.
- APR – only if contraindicated or declined chemoradiotherapy as primary treatment; may be used as salvage.
Three indications for failure:
- Residual tumour – sometimes ulcer remains which can be inflammatory so histology needed to prove residual disease. If extensive invasion, may need exenteration + flap reconstruction.
- Recurrence – multiple biopsies needed (radiotherapy makes histopathological assessment difficult)
- Complications of treatment – e.g. radionecrosis, fistula and incontinence. Radionecrosis pain may require colostomy to divert, or radical APR with flap.
Defunctioning may be required prior to oncological treatment.
- Indications: incontinence, obstruction, perianal sepsis and fistulation.
- Relative indications: local symptoms such as tenesmus or pain – to prevent breaks in treatment.
- Patients informed only 50% of stomas reversed and bowel function may be poor.
Inguinal metastases
- Prophylactic radiotherapy
- Advised for T2-4 tumours due to high risk of recurrence.
- CT and MRI cannot differentiate involved vs uninvolved nodes. PET-CT may help differentiate. Sentinel biopsy may provide alternative – more data required.
- Chemoradiotherapy
- Treatment for all involved nodes.
- Radical lymph node dissection
- Surgery for contraindication to chemoradiation.
- Need histological or cytological confirmation; 50% of lymphadenopathy is inflammatory alone.
- Enlarged groin nodes after primary therapy, then radical groin dissection indicated (50% 5-year survival)
- Discuss fertility options for childbearing age
- Egg/sperm banking.
- Irradiated uterus will not be able to carry foetus to term.