Epithelial Neuroendocrine Neoplasms: Grading Based on the New WHO 2022 Guidelines

Neuroendocrine tumors (NETs) are rare. Epithelial NETs are generally considered slow-growing tumors. Arising from neuroendocrine cells, NETs can develop at various primary sites in the body. Gastrointestinal NETs are the most common of all NETs. The ileum, appendix, and rectum are among the most common sites, followed by the colon, stomach, and duodenum; some series report a female preponderance. Bronchopulmonary NETs are relatively rare and are often indolent in nature. In recent decades, the incidence has been rising. This may be due to greater awareness, improved diagnostic tools, or changes in definitions/classification. Grading of epithelial neuroendocrine neoplasms is beneficial, as it allows tumors to be graded by proliferative activity and distinguished from neuroendocrine carcinomas.