Amanda Charlton, The Children's Hospital at Westmead.
'Standards for classification, staging and grading [8, 9] The World Health Organization (WHO) classification attempts to separate NETs into behavioural categories according to size, depth of invasion and the presence or absence of angioinvasion. This is the most widely used classification system, and should be used in the reporting of NETs until a more definitive classification becomes available. It should be borne in mind that the general principles of the WHO vary for NETs from different sites.
The WHO classification however, does not address the ‘in between’ NETs that are less than well differentiated but are not poorly differentiated and that show an intermediate mitotic rate between low and high.'
I agree with w Liauw above that update is required, the WHO 2010 Classification of tumours of the Digestive system specifically addresses the grading and the "in betweens " into a NET G1, NET G2, NET G3 as explained in a special section in WHO book page 13 and 14.