Grading differences NETs are well-differentiated cancers with different grade categories. NECs are poorly-differentiated cancers - a distinct group with a consistently high Ki67 - and therefore are not routinely assigned a grade (though some may call them Grade 3). NET gradings: • Grade 1 is a well-differentiated cancer with a Ki67 less than 3% • Grade 2 is a well-differentiated cancer with a Ki67 between 3 and 20% • Grade 3 is a well-differentiated cancer with a Ki67 more than 20%
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Histology Image Source: Cuthbertson, Shankland & Sririjaskanthan (2023) Clin Med)
Ki-67 staining of neuroendocrine cancer: (a) grade 1 NET (ileum), (b) grade 2 NET (lung, atypical carcinoid), (c) grade 3 NET (pancreas) (d) NEC (small cell lung cancer)
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