Diabetes and the NET connection

With those diabetes diagnoses numbers, it follows that many NET patients will be diabetic before diagnosis, some will succumb to diabetes whether they have NETs or not.  However …. and here is the NET connection….. some will go on to have an increased risk of succumbing due to their treatment, and some may even be pushed into diabetes as a direct result of their NET type or treatment. It’s important to understand diabetes in order to understand why certain types of NET and certain treatments could have an involvement.

What are the direct connections between Diabetes and NETs?

It’s not surprising that diabetes is mostly associated with Neuroendocrine Tumors of the Pancreas but there are other areas of risk for other types of NETs including to those who are existing diabetics – see below.

Surgery

The main types of surgery for Neuroendocrine Tumors of the Pancreas are Distal Pancreatectomy (tail), Sub-total pancreatectomy (central/tail), Classic Whipple (pancreaticoduodenectomy – head and/or neck of pancreas), Total pancreatectomy (remove the entire pancreas) or an Enucleation (scooping out the tumour with having to remove too much surrounding tissue). From the PERT article link above (exocrine function), you can see why some people need this treatment to offset issues of reduced production of pancreatic enzymes. The same issue can develop with a reduced endocrine function leading to the development of diabetes.

NET Syndromes

The different types of functional pancreatic NETs often called syndromes in their own right due to their secretory role. One might think that Insulinomas are connected to diabetes issues, but this hormonal syndrome is actually associated with low blood sugar (hypoglycemia), although low blood sugar can turn out to be a complication of diabetes treatment.

A NET syndrome known as Glucagonoma (a type of functional pancreatic NET) is associated with high blood glucose levels. About 5-10% of pancreatic neuroendocrine tumors are Glucagonomas, tumors that produce an inappropriate abundance of the hormone glucagon. Glucagon balances the effects of insulin by regulating the amount of sugar in your blood. If you have too much glucagon, your cells don’t store sugar and instead sugar stays in your bloodstream. Glucagonoma therefore leads to diabetes-like symptoms (amongst other symptoms). In fact, Glucagonoma is sometimes called the 4D syndrome – consists of diabetes, dermatitis, deep venous thrombosis (DVT), and depression.

Another functional pancreatic NET known as Somatostatinoma is prone to developing insulin resistance. Somatostatinomas produce excessive amounts of somatostatin which interferes with the insulin/glucagon function and could therefore lead to diabetes.

Diabetes caused by cancer or cancer treatment

Worth noting that this type of diabetes is sometimes known as ‘Pancreatogenic diabetes’ and this is actually classified by the American Diabetes Association and by the World Health Organization as type 3c diabetes mellitus (T3cDM) and refers to diabetes due to impairment in pancreatic endocrine function due to acute cancer and cancer treatment (and several other conditions). The texts tend to point to cancers (and other conditions) of the pancreas rather than system wide. Prevalence data on T3cDM are scarce because of insufficient research in this area and challenges with accurate diabetes classification in clinical practice. (Authors note: Slightly confusing as many texts say that type 3 diabetes is proposed for insulin resistance in the brain (diabetes associated with Alzheimer’s disease).  There’s another term for a complete removal of the entire pancreas – Pancreoprivic Diabetes.

Other treatment risks

Somatostatin Analogues (e.g. Octreotide and Lanreotide) are common drugs used to control NET Syndromes and are also said to have an anti-tumor effect. They are known to inhibit several hormones including glucagon and insulin and consequently may interfere with blood glucose levels. The leaflets for both drugs clearly state this side effect with a warning that diabetics who have been prescribed the drug, should inform their doctors so that dosages can be adjusted if necessary. The side effects list also indicates high and low blood glucose symptoms indicating it can cause both low and high blood glucose (hypoglycemia and hyperglycemia). For those who are pre-diabetic or close to pre-diabetic status, there is a possibility that the drug may push blood tests into diabetic ranges.

Afinitor (Everolimus). The patient information for Afinitor (Everolimus) clearly states “Increased blood sugar and fat (cholesterol and triglycerides) levels in blood: Your health care provider should do blood tests to check your fasting blood sugar, cholesterol and triglyceride levels in the blood before you start treatment with AFINITOR and during treatment with AFINITOR”

Sutent (Sunitinib). The patient information for Sutent (Sinitinib) clearly states that low blood sugar (hypoglycemia) is a potential side effect. It also advises that low blood sugar with SUTENT may be worse in patients who have diabetes and take anti-diabetic medicines. Your healthcare provider should check your blood sugar levels regularly during treatment with SUTENT and may need to adjust the dose of your anti-diabetic medicines.

In rare cases, certain NETs may produce too much Adrenocorticotropic hormone (ACTH), a substance that causes the adrenal glands to make too much cortisol and other hormones. This is often associated with Cushing’s syndrome. Cortisol increases our blood pressure and blood glucose levels with can lead to diabetes as a result of untreated Cushing’s syndrome.

Summary

I think it’s sensible for all NET patients, particularly those with involvement as per above and who are showing the signs of hypoglycemia and hyperglycemia, to be checked regularly for blood glucose and if necessary HbA1c. Many patient information leaflets for the common NET treatments also indicate this is necessary. Always tell your prescribing doctors if you are a diabetic or about any history of low or high blood glucose before treatment for NETs.

My brush with Diabetes (as at Nov 2019)

My blood glucose levels started to climb slightly in 2016 but HbA1c remained normal. However, an HbA1c test in early 2018 put me into pre-diabetic range (44 mmoL/moL). I explained some of the above article to my GP who is corresponding with a diabetes expert at secondary care – the expert suggested that I need to be monitored carefully as weight loss is not necessarily the best response. I have kept my NET team up to date.

At the time of updating, two separate and sequential HbA1c tests (3-month interval) came back normal at 36 mmoL/moL.  I’m pragmatic enough to know that I do not need to lose weight as one of the aims of reducing my blood glucose and HbA1c levels (something emphasised by the above-mentioned diabetes specialist). My Nov 2019 surveillance tests indicate 39 mmoL/moL so still in normal range.

At this point, I cannot yet say if this is the beginning of progressive Type II diabetes or if my medication is causing these spikes in my blood glucose and HbA1c. Judging by 3 x normal HbA1c, looks like the somatostatin analogue (Lanreotide in my case) may have caused a spike to a pre-diabetes score.  I will keep you posted.  Edit:  2022, still in normal range. 

I even got on my bike to do a little bit more exercise just in case!