WHO Classification of Tumours of the Digestive System 1
Bosman FT, Carneiro F, Hruban RH, Theise ND (Eds.)
WHO Classification of Tumours of the Digestive System.
4th Edition
International Agency for Research on Cancer: Lyon 2010

C21 - Anus and anal canal:

Epithelial tumors
    Premalignant lesions
        8077/0 Squamous intraepithelial neoplasia, low grade
        8077/2 Squamous intraepithelial neoplasia, high grade

    Bowen disease
        8542/3 Paget disease, extramammary

        8070/3 Squamous cell carcinoma, NOS
        8051/3 Verrucous carcinoma, NOS
        8020/3 Carcinoma, undifferentiated, NOS
        8140/3 Adenocarcinoma, NOS
        8480/3 Mucinous adenocarcinoma
        8480/3 Pseudomyxoma peritonei with unknown primary site
        8090/3 Basal cell carcinoma, NOS

    Neuroendocrine neoplasms
        8240/3 Carcinoid tumor, NOS
        8240/3 Typical carcinoid
        8240/3 Bronchial adenoma, carcinoid
        8249/3 Atypical carcinoid tumor
        8246/3 Neuroendocrine carcinoma, NOS
            8013/3 Large cell neuroendocrine carcinoma
            8041/3 Small cell carcinoma, NOS
            8041/3 Small cell neuroendocrine carcinoma
        8244/3 Mixed adenoneuroendocrine carcinoma

Other tumours
    8720/3 Malignant melanoma, NOS
    8052/0 Squamous cell papilloma, NOS
    8405/0 Papillary hidradenoma

Secondary tumours