Overview

We all know that Neuroendocrine Tumours (NETs) and their syndromes are complex but there is even more complexity to be found in a group of related disorders known as Multiple Endocrine Neoplasia (MEN).  I recommend all NET patients should try to understand the basics of MEN and vice versa, particularly as both conditions seem to come with a plethora of endocrine-related effects.

MEN patients will normally have a tumour in at least two endocrine glands – thus the terms ‘Multiple’ and ‘Endocrine’ (tumours can also develop in other organs and tissues).  Neoplasia is just another name for tumour and these can be non-cancerous (benign) or cancerous (malignant) with the potential to metastasize.

MEN syndromes can comprise varying combinations of tumours and many will be aware of the tumour risks from family knowledge.  So putting the heredity aspects to one side, it’s potentially an extremely challenging surveillance and subsequent diagnostic scenario if (and when) these risks are realised.  To add to the complexity, some of the associated tumours can be sporadic (non-hereditary) classic Neuroendocrine Tumours in various locations.

MEN Types

MEN is actually an umbrella term for a number of types (syndromes) of the disease – MEN1, MEN2a and 2b (2b was formerly MEN3). There’s a new kid on the block called MEN4 which is extremely rare.

In the most basic of terms regarding the relationship with tumours:

MEN1 seems to be centred on tumours of the parathyroid glands, the pituitary gland, and the pancreas (the 3 P’s). There can be other issues present including various skin issues and manifestations of foregut NETs, typically bronchial or thymic, and sometimes gastric. 

MEN2a mainly focuses on medullary thyroid carcinoma, pheochromocytoma, parathyroid hyperplasia or adenomas (causing hyperparathyroidism), and occasionally cutaneous lichen amyloidosis or Hirschsprung disease (HSCR).

MEN2b is related to medullary thyroid carcinoma (MTC), pheochromocytoma, multiple mucosal neuromas and intestinal ganglioneuromas, and often a marfanoid habitus and other skeletal abnormalities.

MEN4 – A relatively new MEN variant and related to the CDKN1B gene, similar to MEN1 but normally only 2 of the 3 Ps, parathyroid and pituitary. 

What is particularly distinctive with MEN is that they are inherited disorders.   That means that they can be passed down in families, with each child of an affected parent having a 1 in 2 or 50% risk of inheritance. Consequently, genetic screening/testing is normally undertaken in established MEN families and those at risk of MEN.

Associated Types

You may also have heard of other NETs with a familial aspect, in particular Pheochromocytomas (adrenal gland tumours) and Paragangliomas (outside the adrenal gland), Not all are inherited, and I mention them because of the connection with MEN2a and MEN2b.  Read more here – A spotlight on Pheochromocytoma and Paraganglioma

There are other less common connections with NET, mainly Von Hippel-Lindau syndrome (VHL), Neurofibromatosis type 1, Tuberous Sclerosis complex, and various Succinate dehydrogenase (SDHx) syndromes including Carney -Stratakis.