Anal Squamous Cell Carcinoma

Anal squamous cell carcinoma is the dominant anal malignancy and is strongly associated with oncogenic human papillomavirus.

Unlike rectal adenocarcinoma, the primary treatment is sphincter preserving chemoradiotherapy, even for many node positive locally advanced tumours.

Surgery is reserved primarily for salvage of persistent or recurrent local disease.

Presentation includes rectal bleeding, anal pain, a palpable mass, tenesmus or ulceration.

Advanced lesions can invade the vagina, urethra, prostate or surrounding perineal structures.

Palpable inguinal nodes may represent regional metastatic disease rather than distant metastasis.

Confirm histology with biopsy.

Stage with pelvic MRI and CT or PET CT.

Document tumour size, anal canal versus margin location, sphincter involvement and inguinal and pelvic nodal disease.

Localised anal canal disease

Definitive concurrent chemoradiation is standard for most stage I to III anal canal cancers.

A widely used regimen is:

Mitomycin 10 mg/m² IV on days 1 and 29

plus

Fluorouracil 1000 mg/m²/day by continuous IV infusion on days 1 to 4 and 29 to 32

with concurrent pelvic radiation.

An oral fluoropyrimidine alternative is:

Capecitabine 825 mg/m² orally twice daily on radiotherapy days

combined with mitomycin.

Radiation dose is tailored to stage and commonly lies in the range of approximately 45 to 59.4 Gy, with treatment of the primary tumour and appropriate pelvic and inguinal nodal regions.

Response

Do not declare chemoradiotherapy failure too early.

Tumours may continue regressing for several months after treatment. In the absence of clear progression, allow clinical response to mature, with definitive response assessment often continuing toward approximately 26 weeks from treatment initiation.

Salvage surgery

Biopsy proven persistent or locally recurrent disease after adequate chemoradiotherapy requires salvage abdominoperineal resection when an R0 resection is achievable.

Prior radiotherapy causes substantial perineal wound morbidity. Large perineal defects frequently benefit from vascularised flap reconstruction.

Metastatic disease requires systemic treatment and biomarker informed oncology management.