Neuroendocrine Cancer: Ga68 PET Scan – a game changer?

When I was offered my very first Ga68 PET/CT at a 6 monthly surveillance meeting in May 2018, I was both excited and apprehensive. Let me explain below why I had a mix of emotions.

I was diagnosed in 2010 with metastatic NETs clearly showing on CT scan, the staging was confirmed via an Octreotide Scan which in addition pointed out two further deposits above the diaphragm (one of which has since been dealt with). In addition to routine surveillance via CT scan, I had two further Octreotide Scans in 2011 and 2013 following 3 surgeries, these confirmed the surveillance CT findings of remnant disease. The third scan in 2013 highlighted an additional lesion in my thyroid (still under a watch and wait regime, biopsy inconclusive but read on….).

To date, my 6 monthly CT scans seem to have been adequate surveillance cover and all my tumour and hormone markers remain normal. I’m reasonably fit and well for a 62-year-old.

Then I ventured into the unknown

this is not actually my scan!

I wrote a comprehensive post about the Ga68 PET entitled “…. Into the unknown” – so named because that is how I felt at the time. It’s well-known that the Ga68 is a far superior nuclear scan to the elderly Octreotide type, showing much greater detail with the advantage of providing better predictions of PRRT success if required downstream. It has been a game changer for many and if you look below and inside my article, you will see statistics indicating just how it can ‘change the game’ in somatostatin receptor positive Neuroendocrine Cancer diagnostics and treatment.

The excitement of the Ga68 PET

I was going to get the latest ‘tech’ and thought it could be useful confirmation of what I already knew. I also felt lucky to get one, they are limited in UK and there has to be a clinical need to get access. I was excited because it might just rubber stamp the stability I’ve enjoyed for the past 5 or so years since my last surgery in 2012.

The apprehension of the Ga68 PET

I also felt apprehensive because of the ‘unknown’ factor with cancer, i.e. what is there lurking in my body that no-one knows about, and which might never harm me but this scan will light it up demanding attention. I was also apprehensive in case this more detailed scan found something potentially dangerous. As we know, NETs are mostly slow-growing but always sneaky. Of course, any new tumours found may not actually be new, they were just not seen until the Ga68 PET was able to uncover them.  How annoying!

Is the Ga68 PET Scan a game changer?

To confirm the advantages of SSTR PET over Octreotide scans, a study comprising 1,561 patients reported a change in tumour management occurred in over a third of patients after SSTR PET/CT even when performed after an Octreotide scan.

  • Overall, change in management occurred in 44% (range, 16%-71%) of NET patients after SSTR PET/CT.
  • In 4 of 14 studies, SSTR PET/CT was performed after an 111In-Octreotide scan. In this subgroup, additional information by SSTR PET/CT led to a change in management in 39% (range, 16%-71%) of patients.
  • Seven of 14 studies differentiated between inter- and intramodality changes, with most changes being intermodality (77%); intramodality, (23%). (note: intermodality means changes within the same treatment, intramodality means change to another treatment).

In an older study, this slide from a NET Research Foundation conference shows some more interesting statistics:

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This slide from a recent NET Research Foundation conference confirms the power of more detailed scanning

Was Ga68 PET a game changer for me?

Yes, I believe so.  I’m now in the ‘bone met club’ and although that single metastasis has probably been there for some time, it’s not a ‘label‘ I was keen to add to my portfolio. If I was to be 100% honest, I’m not totally convinced it’s a metastasis. The scan has brought more light onto my thyroid issue.  In fact it indicates even more potential issues above the diaphragm including what looks like a new sighting around my left pectoral lymph nodes.  The scan also lghts up a known issue in the left clavicle lymph nodes, first pointed out via Octreotide scan in 2010 and biopsy negative.

In addition to a nuclear scan update (routine surveillance), it also formed part of an investigation into progression of my retroperitoneal fibrosis (initially diagnosed 2010 but potential growth spotted on recent surveillance CT).  The Ga68 PET doesn’t make fibrosis light up (it’s not cancerous) but there are some hotspots in the area of the aorta close to the fibrosis, a potential source if the cause.  Surgery is on hold for now as my kidney function is fine following a renal MAG3 scan which reported no blockages. 

It would appear I’m no longer a boring stable patient

The Ga68 PET Scan confirmed:

Bone Metastases. Report indicates “intense focal uptake“. It always amazes me that people can be thankful for having an extra tumour.  I’m thankful I only have a single bone metastasis (right rib number 11). I had read so many stories of those who got their first Ga68 PET and came back with multiple bone metastases. I’ll accept one and add to my NET CV. I have no symptoms of this bone metastasis and it will now be monitored going forward. I’m annoyed that I don’t know how long it’s been there though!

Confirmation and better understanding of the following:

  1. Thyroid lesion There is some uptake showing. A 2014 Biopsy of this lesion was inconclusive and actual 2018 Ga68 PET report infers physiological uptake. I’m already diagnosed hypothyroidism, possibly connected.  (Edit – on ultrasound in Jan 2019, looks slightly smaller than previous check).
  2. Left Supraclavicular Fossa (SCF) Nodes lighting up “intense uptake“.  I’ve had an exploratory biopsy of the SCF nodes, 5 nodes removed negative. Nothing is ‘pathologically enlarged’ in this area. Monitored every 6 months on CT, annually on ultrasound.  I had 9 nodes removed from the left axillary in 2012, 5 tested positive for NETs and this area did not light up. This whole area on the left above the diaphragm continues to be controversial. My surgeon once said I had an unusual disposition of tumours.  (Edit: Nothing sinister or worryingly enlarged showing on Jan 2019 ultrasound – measuring 6mm).
  3. Report also highlights left subpectoral lymph nodes which is new.  The subpectoral area is very interesting as from my quick research, they are closer to the left axillary (armpit) nodes than they are to the SCF nodes. I’m hoping to get an ultrasound of these in January at my annual thyroid clinic (Edit: nothing sinister showing on ultrasound in Jan 2019).
  4. My known liver metastases lit up (remnant from liver surgery 2011) – not marked as intense though. The figure of 3 seems to figure highly throughout my surveillance scans although the PET report said “multiple” and predominately right-sided which fits.
  5. Retroperitoneal area. This has been a problem area for me since diagnosis and some lymph nodes are identified (intense word not used). This area has been highlighted on my 3 octreotide scans to date and was first highlighted in my diagnosis trigger scan due to fibrosis (desmoplasia) which was surrounding the aorta and inferior venous cava, some pretty important blood vessels. I wrote an article on the issue very recently – you can read by clicking here. So this scan confirms there are potentially active lymph nodes in this area, perhaps contributing to further growth of the fibrosis threatening important vessels – read below.

Retroperitoneal Fibrosis (Desmoplasia)

I have learned so much about desmoplasia since this issue arose that I now fully understand why I had to have radical surgery back in 2010 to try to remove as much of the fibrosis as possible from the aortic area. You can read more about this in my article.  Desmoplasia via fibrosis is still very much of an unknown and mystery condition in NETs.

I now know that my fibrosis is classed as clinically significant and according to the Uppsala study of over 800 patients inside my article, I’m in 5% of those affected in this way (2% if you calculate it using just the retroperitoneal area).

It appears this problem has come back with new fibrosis or growth of existing fibrosis threatening to impinge on blood vessels related to the kidneys and also my ureters (kidney to bladder urine flow). The Ga68 PET doesn’t make fibrosis light up (it’s not cancerous) but there are some hotspots in the area of the aorta close to the fibrosis.

I didn’t expect this particular problem to return – it was a bit of a shock. My hormone markers have been normal since 2011 and this just emphasises the importance of scans in surveillance. 

Conventional Imaging is still important though

There’s still quite a lot of hype surrounding the Ga68 PET scan and I get this.  However, it does not replace conventional imaging (CI) such as CT and MRI scans which still have their place in routine surveillance and also in diagnostics where they are normally at least the trigger for ‘something is wrong’. For the vast majority, a CT/MRI scan will find tumours and be able to measure reductions and progress in regular surveillance regimes. In fact, the retroperitoneal fibrosis has appeared on every CT scan since diagnosis but the changes were highlighted on my most recent standalone CT and it triggered the Ga68 PET (although my new Oncologist did say I was due a revised nuclear scan).  It’s not a ‘functional’ issue (although it is caused by functional tumours). In fact the fibrosis is not mentioned on the Ga68 PET because it is not lighting up – but the lymph nodes surrounding it are mentioned and they are under suspicious as being active.

Appropriate Use Criteria for Somatostatin Receptor PET Imaging in Neuroendocrine Tumors

There are actually recommended usages for the Ga68 PET scan here.  For example, it is not recommended for routine surveillance in place of CI.

Scans – ‘horses for courses’

Read a summary of all conventional scans and nuclear scans by clicking here.

Next Steps

I had a meeting with my Oncologist and Surgeon and a surgical plan is possible in the event of a problem. My surgeon explained it all in his wonderfully articulate and brilliant surgical mind. Fortunately it’s not really urgent but pre-emptive treatment may be required at some point as the consequences of kidney/bladder function are quite severe. Following some further checks, the anticipated surgery is on hold for now as my kidney function is fine following a renal MAG3 scan which reported no blockages.  I continue to have monthly renal blood tests and it was hinted another renal MAG3 could be done at the end of the year.

Summary

My game has changed, that’s for sure. I’m now entering a new phase and I’m waiting on details of my revised surveillance regime. However, at least my medical team and I now know what WE are dealing with and the risks vs benefits are currently being assessed. I’m heavily involved in that.

If you can see it, you can detect it. If you can detect it, you can monitor or treat it.

 

Gallium 68 PET Scans – Into the Unknown

OPINION

Cancer is a growth industry …literally! More people are being diagnosed than ever before. Fortunately, more people are surviving than ever before. This is against a backdrop of better awareness, better screening in the big population cancers, and to a certain extent better diagnostic tools, all of which is leading to earlier diagnosis.

So how does this affect Neuroendocrine Cancer?

According to the latest SEER database figures for Neuroendocrine Cancer, one reason for the 7 fold increase in incidence rates since the 1970s is all of those things above including better diagnostics. This has led to a revised set of epidemiological information in many countries that have made the effort to accurately update their cancer registries and there are consistent reports of incidence rates way beyond the recognised rare thresholds. Another piece of good news is that the increase in NET incidence is also due to earlier diagnosis. To sum that up – NETs is also a growth industry.

Better diagnostics

Combined with more awareness and education (including the important pathologists), more NETs than ever are being found, and many found earlier. However, it’s not party time yet because there remains far too many misdiagnoses due to the low population of the disease and the difficulty in diagnosing it. I want to focus on scanning (thus the title of the article). Whilst there are really important factors involved in a diagnosis, such as tumor and hormone markers, and biopsies (tissue is the issue), a scan is very frequently what triggers many deeper investigations to unearth a NET, i.e. if you can see it, you can normally detect it (whatever the ‘it’ is). And I include the widespread availability and increasing advances in endoscopy/ultrasounds/cameras which have also been instrumental in picking up many Gastrointestinal NETs.

The Gallium 68 PET Scan

There’s a lot of excitement about the Gallium 68 PET Scan since it was approved by the US FDA. It’s not new though and has been in use in several countries for some time. It’s a ‘nuclear scan’ and can often form part of what is known as a ‘Theranostic Pair’ (i.e. in conjunction with a therapy – read more here).

What does it do?

It comprises two main components – a PET scanning machine, and the use of a diagnostic imaging agent which is injected into the person undergoing the scan. Most machines have an inbuilt CT which forms part of the scan. The agent is a somatostatin analogue labeled radionuclide (Gallium 68) and basically the PET will then be used to see where the peptide/radionuclide mix ‘loiters’ (i.e. where there are concentrations of somatostatin receptors (SSTR) normally indicating ‘focal intense abnormality‘ of the type that is regularly found with NETs.

Imaging Agents. There are different agent variants, namely, DOTATATE, DOTATOC and DOTANOC. In USA, you may sometimes see this referred as NETSPOT which is more of a commercial label for the agent (NETSPOT is a DOTATATE). Ga68 PET or SSTR PET are common descriptors for the entire process regardless of the compound. Clearly the scan works best for those with ‘somatostatin receptor positive’ tumours.

These newer agents have several benefits over the elderly In111-pentetreotide (Octreotide scan), including improved detection sensitivity, improved patient convenience due to the 2-3 hour length of the study (compared to 2 or 3 days with Octreoscan), decreased radiation dose, decreased biliary excretion due to earlier imaging after radiotracer administration, and the ability to quantify uptake. The quantification of the uptake can help decide whether a patient is suitable for radionuclide therapy such as PRRT. Eventually, all Octreotide scans should be replaced with SSTR PET but it will take some time (and money).

scans for nets
Octreoscan vs Ga68 PET

To confirm the advantages of SSTR PET over Octreotide scans, a study comprising 1,561 patients reported a change in tumour management occurred in over a third of patients after SSTR PET/CT even when performed after an Octreotide scan. Worth pointing out that SSTR PET is replacing the ageing Octreotide scan and not conventional imaging (CI). You can see the recommended scenarios for use of SSTR PET in this article published by the Journal of Nuclear Medicine. The slide below is interesting, although it was a small study. However, you can see the treatment changes as a result of a Ga68 PET are quite striking.

This slide from a NET Research Foundation conference confirms the power of more detailed scanning

 

Appropriate Use Criteria for Somatostatin Receptor PET Imaging in Neuroendocrine Tumors

I see many people complaining because the cannot get access to a Ga68 PET which is available through their healthcare system or local hospital. Many of these issues are insurance based.  Worth pointing out that there are actually recommended usages for the Ga68 PET scan here.  For example, it is not recommended for routine surveillance in place of Conventional Imaging (CI).

Any pitfalls with Ga68 PET Scan?

When you look at the study data above, it looks like an excellent addition to the diagnostic and surveillance toolkit for NETs. However, 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 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.”

“The highest-intensity physiologic uptake of GaTate is seen in the spleen, followed by the adrenal glands, kidneys, and pituitary gland”

It follows that failure to interpret nuclear scans alongside the patient’s clinical history can sometimes result in two big issues for patients:

1. Unnecessary worry when ‘something’ shows up which is actually a false positive.

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

Just imagine something which is 40 times better than current PET scan technology? That’s what the scientists are working on now. Here’s an example called “EXPLORER“. You can update yourself here. The issue of interpretation will be even more difficult when the new generation of scans appear. There’s an excellent article from Cancer Research UK talking about the modern phenomenon called ‘overdiagnosis’ – read here

Lanreotide and Octreotide and timing the scan?

From the same technical document referred above, here’s an extract (updated to include Lanreotide). “Uptake at physiologic and pathologic sites may change in patients who undergo concomitant short- or long-acting somatostatin analog therapy, which competes with the radiotracer for bioavailability. We generally discontinue short-acting octreotide for 12–24 hours and perform imaging in the week before the next dose of long-acting Octreotide/*Lanreotide, which is typically administered monthly“.  It’s actually the same text as found in the manufacturer’s drug leaflet (click here). More evidence behind the reason for this restriction is found here (please refer to the comments on Ga68 PET – the article also covers the issue of PRRT which is very interesting as a separate subject to the scan timings).

*added by the author for completeness.

Having my first Ga68 PET Scan after 8 years of  living with NETs? 

When I was offered my very first Ga68 PET/CT at my recent 6 monthly surveillance meeting, I was both excited and apprehensive. I was diagnosed in 2010 and my staging was confirmed via an Octreotide Scan pointing out two further deposits (one of which has since been dealt with). I’ve had two further Octreotide Scans in 2011 and 2013 following 3 surgeries. The third scan in 2013 highlighted my thyroid lesion – still under a watch and wait regime. So far, my 6 monthly CT scans seemed to be adequate surveillance cover and my markers remain normal.

I’m apprehensive because of the ‘unknown’ factor with cancer – what is there lurking in my body that no-one knows about and which might never harm me.

I’m excited because it might just confirm that there is nothing new to worry about.

However, I’m both excited (morbidly) and apprehensive because the scan might find something potentially dangerous. As we know, NETs are mostly slow growing but always sneaky. That said, at least I will know and my medical team will know and be able to assess the risk and decide on a course of action.

Doing the Scan

On 5th June 2018, I attended a very experienced Ga68 PET establishment called Guys Cancer Centre in London.  I arrived and was immediately taken under the wing of the nuclear medicine guys who asked me fairly in depth questions about my clinical background.  They then inserted a cannula ready for the injection of the radiolabelled tracer.  I was then installed in the ‘hot room’ where they injected the radionuclide tracer through the cannula and then I had to remain in the hot room for 1 hour to let the tracer circulate.  After 1 hour, I was taken to the PET scanner and it took around 30-35 minutes. Following that I was allowed to leave for home.  It was an extremely easy experience and a significant improvement on doing the 3 day Octreotide scan.

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Door to the ‘hot room’

The Results of the Ga68 PET Scan – CLICK HERE