Grading – Key WHO 2017 Changes

WHO Classifications of Cancer are published in something known in medical world as “The Blue Book”.  For NETs, the 2017 version comprises only the “WHO Classification of Tumours of Endocrine Organs”.  Technically this would preclude the digestive system and lung NETs but I’m told on good authority from world leading pathologists and from listening to lectures at ENETS 2018, that the classification in the leading picture is to be used for all NENs. Worth also noting that the latest ENETS Guidelines are already using the new grading terms.  Many sites remain out of date so be careful where you look.

The 2017 World Health Organisation (WHO) classification sub-divided Grade 3 into two new entities: a well differentiated high-grade NET and a poorly differentiated high-grade NEC.  There may also be a cut-off point in proliferative rate (i.e. Ki-67) between NET and NEC in relation to potential treatment strategies (55% is mentioned for pNETs but I’m currently investigating).

The Grade 1 to 2 Ki-67 cut-off is changed from 2 to < 3 for clarification purposes.  There was some discussion as to whether it should be <5 but this was not accepted.

Well differentiated High Grade NETs are now recognised.  These are known as a NET rather than a NEC.  Both Grade 3 (NET) and Grade 3 (NEC) have the same biopsy marker cut-offs as per the leading slide but it is thought that a threshold reading of 55% could have some influence on the treatment regime. For example, a well differentiated tumour with a Ki67 of less than 55% might benefit from the same treatment given to Grade 1 or 2 patients, whereas a well differentiated tumour with a Ki67 of more than 55% might benefit from the same treatment given to poorly differentiated NEC. Only a guideline and I suspect this is like many things in NENs, very individual, relies on many factors, so your specialist will drive this accordingly.  You may see these 2 grades listed as Grade 3a for NET and Grade 3b for NEC.

Previously, Pheochromocytoma did not have an official grading regime, i.e. they were just benign or malignant.  Now they are using the same grading system as above.  I’m assuming this is the same for Paraganglioma and I will confirm in due course.  This is an excellent change and a continuation from the WHO 2010 classification where there was great emphasis away from a benign/malignant classification to formal grade levels on the basis that all NETs have malignant potential.

It also introduced a change to the naming of mixed cell tumours from Mixed AdenoNeuroendocrine Carcinoma (MANEC) to Mixed Neuroendocrine Non-Neuroendocrine Neoplasms (MiNEN).  A full explanation of this MiNEN will follow but I would suggest the use of the term ‘Neoplasm’ has been chosen rather than ‘Carcinoma’ is because these neoplasms can be well or poorly differentiated.

It’s not possible at this time to acquire copies of the official output but I will keep this blog live.

The source material for the 2017 version of this article.

From leading Pathologist Dr Anthony Gill  – Remember this is based on Endocrine Organs only but it will eventually apply to all.   I am awaiting access to free documentation to update this article further – only ones I can currently find are not free!

Misc Grading Issues

The proliferative rate can be diverse in NENs, so sampling issues can limit the accuracy of grading. More substantial samples of tumour are therefore preferable for grading thus why the Ki-67 index is preferred for biopsies where large amounts of tissue may not be available. The distinction of low-grade from intermediate grade can be challenging when using small samples. A couple of interesting observations about NET grading which I spotted during my research and ‘forum watching’.  You can have multiple primary tumours and these might have different Ki-67 scores.  Additionally, on larger tumours, Ki-67 scores can be different on different parts of the tumour.  And something I know from my own experience, secondary tumours can have different Ki-67 scores than primary – even a different grade.  In my own case, my liver secondary tumours were graded higher than my primary which according to my surgeon is in keeping with a clone of the disease having become more aggressive over time.  Royal Free Hospital NET Centre indicates a person’s grade should be taken from the highest biopsy grade taken. This is a fairly complex area but a recent study published by the US National Institute of Health and many anecdotal comments made by NET specialists indicates that is a fairly common scenario.

Staging is the extent or spread of disease.  Most types of cancer have 4 stages, numbered from 1 to 4 indicating a rising spread as the number is bigger. Often doctors write the stage down in Roman numerals, perhaps this is to stop any confusion between standard numbers used for Grades? So you may see stages written as I, II, III and IV.  In addition to this standard method, there is also an agreed model known as TNM (Primary Tumour, Regional Node, Distant Metastasis) which is essentially a more detailed staging definition when combined with the Stage 1-4 model.  Please note with TNM models, there could be different stage descriptions depending on the location of the primary tumour and similarly different TNM models for different tumour locations.

WHO 2017 changes

WHO 2017 has recommended enhancements to the TNM system mainly the use of additional suffixes indicating the extent of lymph node involvement. Details to follow when I can free access.

The following example shows the stage descriptions for a NET of the small intestine (the others are similar but worded accordingly for that part of the anatomy):

Stage I tumour is less than 1 cm in size and has not spread to the lymph nodes or other parts of the body.

Stage II tumour is greater than 1 cm in size and has started to spread beyond the original location, but has not spread to the lymph nodes or other parts of the body.

Stage III is any size tumour that has spread to nearby areas of the body and also to at least one lymph node.

Stage IV is any size tumour that has spread to one or more lymph nodes and has also spread to other, more distant areas of the body (such as the liver).

It’s also worth pointing out that Stage IV does not necessarily mean a cancer is more dangerous than other cancers of lesser stages.  This is an important point for NETs where Stage 4 can be matched up with a low-grade tumour i.e. Stage 4 for lower grade NETs is very often not the ‘red flag’ it is for other more aggressive cancers.  For example, doctors may surgically remove a Stage IV NET, while surgery might not help a patient with a cancer of a higher grade at such a late stage.

Notes:

• Sometimes doctors use the letters to further divide the number categories – for example, stage 2A or stage 3B.  This is normally to clarify or provide more detail of the primary tumour size/invasion in conjunction with the TNM model.
• You may also see something called Stage 0 which is for ‘Carcinoma in situ’. It means that there is a group of abnormal cells in an area of the body. However, the number of abnormal cells is too small to form a tumour and may, therefore, be currently classed as benign.  The World Health Organisation (WHO) system does not appear to recognise Stage 0 for NETs.

The most generic model for TNM staging is below but please note this could be adjusted for particular types of NET.

Primary Tumor (T)
TX: Primary tumor cannot be evaluated
T0: No evidence of primary tumour
Tis: in situ (abnormal cells are present but have not spread to neighbouring tissue; although not cancer, in situ may become cancer and is sometimes called preinvasive cancer)

T1, T2, T3 and T4 is a measure of the size of, and/or invasion/penetration by, the primary tumour and the wording varies between different NET sites. e.g. for a small intestinal NET:

T1 tumour invades mucosa or submucosa and size <=1 cm

T2 tumour invades muscularis propria or size >1 cm

T3 tumour invades subserosa

T4 tumour invades the visceral peritoneum (serosa)/other organs

For any T add (m) for multiple tumours

Regional Lymph Nodes (N)
NX: Regional lymph nodes cannot be evaluated
N0: No regional lymph node involvement
N1: regional lymph node metastasis

Distant Metastasis (M)
MX: Distant metastasis cannot be evaluated
M0: No distant metastasis
M1: Distant metastasis is present

You may occasionally see TNM staging be prefixed by lower case letters.  The most commonly used prefix is ‘p’ simply meaning the grading has been confirmed by pathology.  e.g. pT4 N1 M1

Specialists can combine the Stage to create a TNM – for example: