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WHO Classification of Tumours
Neuroendocrine carcinoma, NOS
Anus and anal canal


Definition

Neuroendocrine carcinoma (NEC) is a poorly differentiated, highgrade malignant neoplasm composed of small cells or large to intermediate cells, sometimes with organoid features resembling neuroendocrine tumour (NET), diffusely expressing the general markers of neuroendocrine differentiation (diffuse expression of synaptophysin; faint or focal staining for chromogranin A), with marked nuclear atypia, multifocal necrosis and a high number of mitoses (> 20 per 10 HPF); high grade (G3) defined according to the proliferation fraction and histology. This definition refers to neoplasms previously classified as small cell carcinoma, large cell (neuro)endocrine carcinoma, or poorly differentiated (neuro)endocrine carcinoma.

Commentary: Neuroendocrine tumours of the digestive system

Topographic definition of the anal canal, anal margin and perianal region