However, the exact cut-off criteria between G1-3 NETs may differ depending on primary site. For example, in lung - where well-differentiated tumours are often referred to as either typical or atypical carcinoids, rather than NETs - the cut off is: • Typical carcinoid: A well-differentiated lung neuroendocrine cancer with a Ki67 of less than 5% would be considered low-grade. • Atypical carcinoid: A well-differentiated lung neuroendocrine cancer with a Ki67 between 5 - 30% may be considered moderate-grade. • NEC: poorly-differentiated, either small or large cell carcinomas, with a Ki67 more than 30%.
La Rosa (2023) Endocrine Pathology (2023) 34:79–97)
The importance of accurate grade cannot be over- emphasised as it is a key determinant of both treatment planning and decision-making, alongside prognosis (where prognosis is the prediction of the most likely course of disease as well as the treatment response)
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