The terms functional and non-functional come up a lot in documents describing Neuroendocrine Cancer.  They also feature highly in patient groups.  But what do these terms actually mean? 

Functional / Non-Functional

Neuroendocrine Tumours are treatable for most but the difficult part can be arriving at a diagnosis. Moreover, some Neuroendocrine Tumours (NETs) can be silently growing and as they grow slowly, the ‘silence’ can go on for some years. Even with a syndrome, the root cause can remain disguised as the symptoms are similar to many day-to-day illnesses.  There can be the odd exception but in general terms, NETs are either functional (with a syndrome) or non-functional (no syndrome). It’s also possible that patients can move from one state to another.  

• Non-functioning tumours—no specific clinical syndrome is observed or excess hormone secretion isn’t sufficient enough to cause symptoms. Worth pointing out that if a particular hormone is out of range but the patient is asymptomatic, that does not necessarily mean the tumour is functional.  There will most likely be some correlation between how much a hormone is out of range and the manifestation of the clinical syndrome. 

• Functioning tumours—the tumours’ secretions lead to distinct clinical symptoms due to elevated levels of the associated hormone(s), some more distinct than others.

Diagnostics

NETs are a difficult cancer to diagnose.  The presence of a functional tumour can have some advantages …. but  only if the person diagnosing the symptoms thinks outside the box. Often it takes perseverance by the patient, carefully explaining the symptoms.  At primary care, this can be challenging given the commonality of certain symptoms with many common conditions.  Sometimes it just needs a routine blood test that can often lead to imaging checks, often done at secondary care – and that is where most diagnoses of NET takes place.  However, many people will have multiple visits and go through several common illness diagnoses (albeit preliminary in many cases) before NET is confirmed. Not many NET diagnoses happen in primary care. 

Syndrome and Tumours – ‘Chicken or Egg’ ?

I’m always confused when someone says they have been diagnosed with a Syndrome rather than a NET type.  You normally need a tumour to produce the symptoms of a syndrome.  The exception to this rule might be hereditary syndromes e.g. MEN.  MEN syndromes are genetic conditions, although they may also lead to functional tumours.