Anorectal mucosal melanoma

Anorectal melanoma is an uncommon and aggressive mucosal melanocytic malignancy. Due to its rarity, the pre-operative diagnosis remains difficult. The first symptoms are non-specific such as anal bleeding, anal mass or pain. Although anorectal melanoma carries a poor prognosis; optimal therapeutics strategies are unclear. Surgical resection remains the mainstay of treatment. The optimal surgical procedure for primary tumours is controversial and can vary from wide local excision or endoscopic mucosal resection (EMR) to an abdomino-perineal resection. A high degree of uncertainly exists regarding the benefit of radiation therapy or chemotherapy. The treatment of advanced melanoma is evolving rapidly with better understanding of the disease biology and immunology. Considerable effort has been devoted to the identification of molecular determinants of response to target therapies and immunotherapy.

New insights into the development and differentiation of the human anorectal epithelia. Are there clinical consequences?

PURPOSE

The epithelial lining of the anorectum still raises discussions concerning the levels of transition between the various zones and leads to an incomplete understanding of the immmunoprofile of rectal carcinoma. Since the expression of cytokeratins depends on the epithelial cell-type and the parahox-gene CDX2 is important for the development of the colorectal epithelium, we investigated different cytokeratins and CDX2 in the anorectum of human prenatal stages and in adult normal and neoplastic anorecta.

MATERIALS AND METHODS

The differentiation and spatiotemporal distribution of the epithelial zones were examined in 33 human embryos and fetuses, in a 2-year-old child and four adults. In comparison, 17 specimens of ultralow rectal adenocarcinoma and 4 specimens of anal carcinoma were investigated. Monoclonal antibodies were directed against cytokeratin (CK) 18, 20, 7 and 14 and CDX2.

RESULTS

Due to the cytokeratin profile and to CDX2 expression, the different anorectal zones could already be differentiated in human prenatal life. We showed that anorectal epithelial differentiation including the squamous epithelia ran in a craniocaudal direction, and that the anorectal zone was a transitional zone between rectal zone and anal transitional zone where CK 7, 18, 20 and CDX2 are simultaneously expressed. All cases of rectal adenocarcinoma showed positivity for CK 18, 20 and CDX2, and three also labelled for CK 7, whereas CK 14 was only expressed in the cases of anal carcinoma.

CONCLUSIONS

Our results elucidate the connection between the prenatal pattern and the origin of the different types of anorectal carcinoma.