📖 About
- Anal cancer is a rare malignancy, more common in HIV-positive men who have sex with men (MSM).
- The anal canal is ~4 cm long, extending from the rectal ampulla to the anal verge.
- The dentate line separates squamous (anal) from columnar (rectal) epithelium – important for pathology & management.
⚠️ Aetiology & Risk Factors
- Incidence: ~1 per 100,000, but rising with HPV prevalence.
- HPV infection (esp. type 16, 18) – strongest association.
- HIV infection increases risk significantly.
- Other risks: smoking, chronic inflammation (fistula, Crohn’s disease), immunosuppression, receptive anal intercourse.
🩺 Clinical Presentation
- Peak age: 50s–60s.
- Symptoms: rectal bleeding, anal pain, palpable lump/swelling, perianal itching, discharge, warts.
- Advanced disease: ulceration, faecal incontinence, inguinal lymphadenopathy, weight loss.
- Exam: irregular mass at anal verge or within canal; always perform DRE + inguinal node palpation.
🔎 Investigations
- Bloods: FBC (anaemia), U&E, LFTs (mets).
- Endoscopy: Proctoscopy ± sigmoidoscopy with biopsy.
- Endoanal ultrasound (EUS): assess depth of invasion.
- Cross-sectional imaging: CT chest/abdomen/pelvis ± MRI pelvis for staging.
- Tissue immunotyping: confirm histological subtype, HPV status may be relevant.
🧬 Pathology
- 🔹 Squamous cell carcinoma (80%) – “epidermoid carcinoma”; HPV-driven.
- 🔹 Adenocarcinoma – upper anal canal, may cross dentate line (often treated like rectal cancer).
- 🔹 Malignant melanoma – aggressive, often pigmented/bleeding lesion.
- 🔹 Basal cell carcinoma – rare, indolent course.
- 🔹 Lymphoma – linked to immunosuppression, esp. AIDS.
- 🔹 Kaposi’s sarcoma – HIV/AIDS-related, vascular lesion.
💊 Management
- All cases discussed at a Colorectal MDT.
- Small, early lesions – local excision ± radiotherapy.
- Standard of care – combined chemoradiotherapy (Nigro protocol: 5-FU + mitomycin C + RT).
- Surgery (abdominoperineal resection, APR) – reserved for salvage or sphincter-destructive tumours not controlled by chemoradiotherapy.
- Clinical trials encouraged due to ongoing optimisation of protocols.
- Palliative care for advanced or recurrent disease (pain relief, stoma formation, radiotherapy for bleeding).
🌟 Exam Pearl: Anal squamous cell carcinoma is HPV-driven and treated primarily with chemoradiotherapy, unlike rectal adenocarcinoma where surgery dominates.
📚 References
- 🧓 Case 1 – Age 68: Retired teacher with a 6-month history of rectal bleeding, perianal pain, and sensation of a lump. Examination revealed an ulcerated lesion at the anal margin with induration.
Investigations: Biopsy confirmed squamous cell carcinoma (SCC) of the anal canal. MRI pelvis and CT chest–abdomen–pelvis showed no distant spread.
Management: Combined chemoradiotherapy with mitomycin and 5-fluorouracil (Nigro regimen) achieved complete remission.
Teaching point: Most anal cancers are SCCs linked to HPV infection and respond well to organ-preserving chemoradiation.
- 🚺 Case 2 – Age 56: Woman with chronic pruritus ani and intermittent bleeding. Examination found a small nodular lesion near the dentate line.
Investigations: Biopsy revealed anal canal adenocarcinoma. Staging showed local invasion into the internal sphincter.
Management: Treated with abdominoperineal resection (APR) following MDT discussion.
Teaching point: Adenocarcinomas of the anal canal are rarer, behave more like rectal cancers, and often need surgical excision.
- 🏳️🌈 Case 3 – Age 49: HIV-positive man with anal pain and bleeding. Digital rectal exam found an irregular mass.
Investigations: Biopsy confirmed high-grade squamous intraepithelial lesion (AIN-III) progressing to invasive SCC.
Management: Chemoradiotherapy with close follow-up and HPV vaccination offered.
Teaching point: HIV infection and receptive anal intercourse increase the risk of HPV-related anal carcinoma; early screening is essential.