2. Uptake Pitfalls (Not everything that lights up on a scan is cancer or NET (chant it 3 times!)

This phenomenon is well-known and well-documented.  There’s a perception among patients that anything with uptake is abnormal. However, this is not always true and can cause unnecessary alarm and concern. I’m going to refer to the output from someone who I believe is a leading authority on this subject. 

One of the challenges with modern scanning equipment and techniques is the ability to correctly interpret the results – in my opinion, this is almost as important as the efficiency of the machines and radionuclides. This requirement has been acknowledged in many articles and I particularly like this technical paper from a very experienced nuclear medicine physician Professor Michael Hofman from the Centre for Cancer Imaging at the Peter MacCallum Cancer in Melbourne. I had a chat with Professor Hofman who added that this is a very sensitive scan, so often picks up “new” disease, which isn’t really new, just never identifiable on standard imaging. However, there’s an excellent section on pitfalls in interpretation and I’m quoting an abstract below.  Although this document is mainly talking about Ga68 PET/CT for NETs, the majority of these pitfalls will generally apply to most SSTR PETs.

“Although GaTate PET/CT is a highly sensitive and specific technique for NETs, the attending physician or radiologist must be aware of various physiologic and other pathologic processes in which cellular expression of SSTR can result in interpretative error. Most of these processes demonstrate low-intensity and/or nonfocal uptake, in contrast with the focal intense abnormality encountered in NETs. Causes of interpretative pitfalls include prominent pancreatic uncinate process activity, inflammation, osteoblastic activity (degenerative bone disease, fracture, vertebral hemangioma), splenunculi or splenosis, and benign meningioma.  Moderately intense uptake is also seen in the liver, salivary glands, and thyroid gland.” and “The highest-intensity physiologic uptake of GaTate is seen in the spleen, followed by the adrenal glands, kidneys, and pituitary gland” 

This has recently been reinforced in the latest set of guidelines published in February 2023 by The Society of Nuclear Medicine and Molecular Imaging (SNMMI) SNMMI Procedure Standard/EANM Practice Guideline for SSTR PET: Imaging Neuroendocrine Tumors (click blue link to read more)

It follows that failure to interpret nuclear scans alongside the patient’s clinical history and tempered by the known behaviours of Neuroendocrine Neoplasms can sometimes result in two big issues for patients:

1. Unnecessary worry when ‘something’ shows up.

2. Something which leads to irreversible treatment when it is not required.

Short extract of interpretative pitfalls in this table:

You can see from above there is physiological uptake. Normal uptake of PET tracers occurs in many sites of the body and may cause confusion in interpretation, particularly in oncology imaging. Osteoblastic and Inflammatory conditions can also light up given concern.   Finally, other tumours that can light up (many benign) and can be incidentally diagnosed, mainly Meningioma which is known to have somatostatin receptors. 

Finally, just to point out there can also be false positives in conventional imaging.