When reading articles in the mainstream media, found in medical publications; and even listening to doctors speak about my disease, it’s clear that the focus is on the term “Neuroendocrine Tumours” or NET for short. Many websites of advocate foundation organisations and specialist scientific organisations, all still use the term “NET” in their naming. I too am guilty of having a large Facebook site falling into this category. It’s little wonder that those with high grade disease can often feel like the forgotten patient group. Clearly all the aforementioned organisations support all patients regardless of grade, but it’s true to say that the naming and general use of terminology continues to fall behind. It’s also true that the term NET remains applicable to the majority of patients and that many use it as a convenience when they actually mean all types including Neuroendocrine Carcinoma. Nonetheless, context remains an important part of overall understanding and inclusivity – words and acronyms matter.
However, High grade or Grade 3 is no longer just Neuroendocrine Carcinoma (NEC). Things have changed since 2017.
What are Neuroendocrine Neoplasms?
Neuroendocrine neoplasms (NENs) are without doubt a heterogeneous (i.e. diverse) bunch of tumours with a common phenotype (i.e. the physical appearance or biochemical characteristic). However, there are two fundamentally different groups of NENs: well-differentiated, low-proliferating NENs, called neuroendocrine tumours (NETs), and poorly differentiated, highly proliferating NENs, called neuroendocrine carcinomas (NECs). The difference between well and poorly differentiated has been described as a ‘dichotomy’, most likely due to the origin from different neuroendocrine progenitor cells (i.e. source cells). Should the term Neuroendocrine Neoplasm be used more? Yes, probably. But should we perhaps also ask if ENETS and NANETS will change their names to ENENS and NANENS?
This revised classification is not recent as many are currently suggesting. These changes were covered in my Staging and Grading article produced in early 2017 and confirmed Neuroendocrine Neoplasms (or NENs) was the overarching term for all types of neuroendocrine disease. See graphic below.
Traditionally, any proliferation score over 20% on the Ki-67 proliferation index (or over 20 mitoses/10 HPF on the Mitotic Index) would have been deemed a Neuroendocrine Carcinoma. However, in the pancreas, NETs and NECs may overlap in their proliferation index, making the distinction between them difficult and leading to treatment uncertainties.
In 2017, the Endocrine ‘Blue Book’ of cancer classification systems introduced a new pancreatic NET category based on a Grade 3 tumour which is well differentiated (i.e. cancer cells look more like normal cells and tend to grow and spread more slowly). While all classifications for all NENs recognise the existence of the two major groups (NET and NEC), there are proposals to develop common NEN classification across all the ‘Blue Books’ and future versions will reflect these changes. The most interesting change will be in the Lung classification because high grade NENs can be small cell or large cell and it’s probably the most controversial grouping.
Interestingly, ENETS guidelines already use the term across the board in their 2016 series (i.e. in advance of the 2017 changes). These changes are part influenced by the results of the NORDIC NEC study which showed that although patients with a Ki67 <55% were less responsive to platinum-based chemotherapy (i.e. drug names ending in ‘platin’ such as Cisplatin, Carboplatin, Oxaliplatin), they had a longer survival, and concluded that not all NEC should be considered as one single disease entity. Also worth noting that the NORDIC NEC study covered many different areas of the anatomy, not just the pancreas. Some of the rationale for the division of grade 3 into well differentiated NETs and poorly differentiated carcinomas is that some grade 3 tumours which are classified into this category according to the Ki67 index percentage, have been recognised to behave more like grade 2 NETs rather than aggressive carcinomas. The inference is that there could be treatment and prognostic significance if a patient is a Grade 3 NET.
MANEC vs MiNEN
Added for completeness. This mixed and rare neoplasm type has traditionally been related to NEC but in 2017 the nomenclature change to a new term was necessary to reflect the fact that some of the tumours involved were not carcinomas or adenocarcinomas but rather were well differentiated tumours or even adenomas (i.e. benign). Previously known as Mixed AdenoNeuroendocrine Carcinoma (MANEC), they were renamed to Mixed Neuroendocrine Non-Neuroendocrine Neoplasms (MiNEN).
MiNEN are neoplasms with two distinct neuroendocrine and non-neuroendocrine cell populations. They can be morphologically classified into three entities: collision, composite, and amphicrine MiNEN. Currently, both components composing a MiNEN must represent at least 30% of the whole tumour. Diagnosis of MiNEN is usually facilitated by the presence of at least one well-differentiated component which may be the Neuroendocrine or Non-Neuroendocrine component. However, the two components may be difficult to identify with conventional morphological techniques, particularly when they are poorly differentiated, and their identification may require additional immunohistochemical techniques. MiNEN usually originate from organs that contain neuroendocrine cells and in which “classical” NENs are known to develop, such as pancreas, appendix, colon, and to a lesser degree small intestine. Other locations in my source document includes Oesophagus, Stomach, Bilary Tract and Gallbladder, Duodenum and Ampulla of Vater and Rectum.
NEC vs NET
Having researched widely, I believe there are 8 key differences between NET and NEC:
- Grade – NEC is only Grade 3, NETs can be Grade 1, 2 or 3.
- Differentiation – all NETs are well differentiated, NECs are poorly differentiated. Important difference at Grade 3.
- Aggressiveness – Most NETs tend to be indolent or slow growing while NECs tend to be aggressive and faster growing. However, Ki67 and/or mitotic count is an aggressiveness measurement tool. Genetic profiles can also be a guide but this is beyond the purposes of this article but may be explored in subsequent parts. It follows that NECs normally have a worse prognosis in comparison to NETs.
- Hormone Secretion – NETs can produce peptide hormones that may be associated with hormonal syndromes. NECs usually fail to express hormones or produce hormonal syndromes.
- Somatostatin Receptors – A NET is much more likely to express somatostatin receptors which can influence treatments such as somatostatin analogues and peptide receptor radiotherapy (PRRT)
- Hereditary Syndromes – NETs are much more likely to be associated with hereditary syndromes such as Multiple Endocrine Neoplasia (MEN).
- Platinum Based Chemotherapy – NETs are less likely to show a good response to platinum based chemotherapy which can often be the first line treatment for NEC.
- Primary Locations – can be vastly different in terms of commonality and therefore provide clues to investigators. Common locations for NEC include: Lung, Esophagus, Colon, Urogential Organs and Skin – with the exception of Lung, these are very rare locations in NETs. Conversely, rare/very rare locations for NEC but common in NET include: Rectal, Small Intestine, Appendix, Stomach, Pancreas.
I intend to cover more on Grade 3 tumours going forward and a ‘Part 2’ article will follow covering treatment differences, genetic profiles and unmet needs.
In addition to my own knowledge gained over the years of researching and writing, the following resources were key in establishing the facts used in compiling this article:
1. Sorbye H, Welin S, Langer SW, Vestermark LW, Holt N, Osterlund P, et al: Predictive and prognostic factors for treatment and survival
in 305 patients with advanced gastrointestinal neuroendocrine carcinoma (WHO G3): the NORDIC NEC study. Ann Oncol 2013; 24: 152–160
2. de Mestier L, Cros J, Neuzillet C, Hentic O, Egal A, Muller N, Bouché O, Cadiot G, Ruszniewski P, Couvelard A, Hammel P: Digestive System Mixed Neuroendocrine-Non-Neuroendocrine Neoplasms. Neuroendocrinology 2017;105:412-425. doi: 10.1159/000475527
3. Koppel G: Neuroendocrine Neoplasms: Dichotomy, Origin and Classifications. Visc Med 2017;33:324-330. doi: 10.1159/000481390
4. Rindi G, Klimstra DS, Abedi-Ardekani B, et al. A common classification framework for neuroendocrine neoplasms: an International Agency for Research on Cancer (IARC) and World Health Organization (WHO) expert consensus proposal. Mod Pathol. 2018;31(12):1770–1786. doi:10.1038/s41379-018-0110-y
Thanks for reading