Updated: 2 March 2005

1) Clinico-pathologic Considerations

The majority of anal malignancies are squamous cell cancers. Keratinizing squamous cancers generally arise in the lower anal canal and non-keratinizing cancers, which are also called cloacogenic, basaloid, or transitional cell anal cancers, predominate in the transitional zone between the dentate line and the junction with the rectal mucosa. The behaviour of keratinizing and non-keratinizing squamous anal cancers, and the approach to their treatment are similar. Metastases most commonly follow lymphatic drainage patterns. Lesions arising above the dentate line can spread to the perirectal and paravertebral nodes, while lesions arising below the dentate line spread to the femoral and inguinal nodes. Distant metastases, predominantly to the lung and liver, occur in more than 10% of those treated¹.

Other anal malignant histologies, including Bowen's or Paget's disease (high grade intraepithelial neoplasia) occur rarely. Treatment principles for these are based on adequate local excision.

Adenocarcinomas can arise from the anal ducts or glands. These should be treated as low-rectal adenocarcinomas as the outcomes are believed to be very similar².

Squamous and basal cell cancers of the perianal skin should be treated as skin cancers with local excision being the mainstay of treatment.

Anal melanomas have very poor outcomes and may require very aggressive surgical management. These cases should be discussed with a member of the skin or melanoma tumour group³.

References:

1. Bartelink H, Roelofson F, Eschwege F, et al. Concomitant radiotherapy and chemotherapy is superior to radiotherapy alone in the treatment of locally advanced anal cancer: results of a phase III randomized trial of the EORTC radiotherapy and gastrointestinal cooperative groups J Clin Oncol 1997; 15:2040-49
2. Perkowski PE, Sorrells DL, Evans JT, et al. Anal duct carcinoma: case report and review of the literature. Am Surg 2000; 66: 1149-52
3. Brady MS, Kavolius JP, Quan SH. Anorectal melanoma: a 64-year experience at Memorial Sloan-Kettering Cancer Center. Dis Colon Rectum 1995; 38: 146-51

2) Radiology/ Imaging

A physical exam is the most important determinant of local spread. However, pelvic and abdominal CT and/or MRI as well as chest X-ray may be of value in assessing both local and metastatic extent of disease. This is particularly relevant for high lesions as the lymphatic drainage can include the paravertebral nodal chains. Endorectal ultrasound may be of value in determining depth of invasion, invasion of adjacent structures, circumferential involvement, and size of tumour. Inguinal adenopathy may be detected on CT scan and may be amenable to needle biopsy, if suspicious for disease. Functional imaging with 18-fdg PET is not widely available or routinely recommended but may have a role in assessing indeterminate lesions seen on other imaging.