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:

wp-image-991783422jpg
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 of 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 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 suspicion of 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 malfunction 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.

 

Neuroendocrine Cancer: Fibrosis – an unsolved mystery?


Background

It has long been observed that certain Neuroendocrine Tumours (NETs) are often associated with their ability to secrete hormones and these substances are thought to be responsible for the collection of symptoms which include (but not limited to) diarrhea, flushing and wheezing.  One of the lesser known aspects of this disease is the development of fibrosis, both local and distant. These fibrotic complications may lead to considerable morbidity. They can also result in incidental diagnoses of NETs after causing abdominal obstructions.

The most well known form of fibrosis is ‘Hedinger Syndrome’ (so-called Carcinoid Heart Disease) tightly associated with midgut NETs and will not be covered further. However, mesenteric fibrosis is actually more common and also associated with midgut NETs.  There are other less common locations involved including retroperitoneal fibrosis, pleural and pulmonary fibrosis and skin fibrosis.

According to a paper (abstract linked below) by Professor Martyn Caplin (et al) regarding mesenteric fibrosis, “it often has a characteristic appearance of a mesenteric mass with linear soft tissue opacities radiating outward in a “wheel spoke” pattern associated with distortion of the surrounding tissues” (see graphic below).

The mesentery and retroperitoneum areas

The mesentery and retroperitoneum are complex to describe but think of the mesentery as something holding the small intestine together with all its folds and the retroperitoneum describes the part of the abdomen that is generally closer to your backbone than to your belly button, i.e. behind the intestines.

Often labelled ‘Desmoplasia’, it is easily spotted on CT and MRI scans and is one of the unusual features of NETs vs other types of cancer.  Some examples are below:

Desmoplastic-reaction-The-characteristic-desmoplastic-reaction-comprises-a-mesenteric
Desmoplastic reaction. The characteristic desmoplastic reaction comprises a mesenteric mass (black asterisks) with linear soft tissue opacities radiating outwards in a ‘spoke-wheel’ or stellate pattern (black arrows) and associated indrawing of the surrounding tissues . Distortion and retraction of the adjacent soft tissues results in kinking of the small bowel and can cause partial or complete bowel obstruction. The mesenteric mass is often associated with coarse calcification (black arrowhead).  
Metastatic-carcinoid-tumor-to-the-root-of-the-mesentery-arrow-causing-typical
Metastatic Neuroendocrine Tumor to the root of the mesentery (arrow) causing typical circumferential desmoplastic

Axial CT image of a patient with a metastatic neuroendocrine tumor that demonstrates retroperitoneal thickening and fibrosis (arrow).

Small intestinal neuroendocrine tumor with characteristic serosal fibrosis causing kinking of the bowel wall (hematoxylin-eosin, original magnification 3 1; scanned slide) Grin, Andrea & Streutker, Cathy. (2015). Neuroendocrine Tumors of the Luminal Gastrointestinal Tract. Archives of pathology & laboratory medicine. 139. 750-756. 10.5858/arpa.2014-0130-RA.

What causes it, what problems does it cause and how can it be treated?

As with Hedinger Syndrome, which mostly causes right-sided fibrosis in the heart, mesenteric and retroperitoneal fibrosis (and others) is thought to be caused by the excess secretion of serotonin (5-HT) from NETs. I say ‘thought’ but no-one really knows for sure.  There’s a few quite recent studies on the subject which I’ll provide abstracts here.

Uppsala Hospital Sweden. In one study entitled “Clinical signs of fibrosis in small intestinal neuroendocrine tumours” first published in November 2016 by Uppsala Hospital Sweden, it said that it was caused by serotonin and other cytokines released from tumour cells and which may induce fibrosis, leading to carcinoid heart disease and abdominal fibrotic reactions. A cohort study of patients with SI NETs diagnosed between 1985 and 2015 was carried out – a total of 824 patients. Clinically significant abdominal signs and symptoms of fibrosis occurred in 36 patients. Of these, 20 had critically symptomatic central mesenteric fibrosis causing obstruction of mesenteric vessels, and 16 had retroperitoneal fibrosis causing obstructive uropathy with hydronephrosis (the swelling of a kidney due to a build-up of urine).  Extensive fibrosis causing mesenteric vessel obstruction and/or obstructive uropathy was more often associated with symptomatic and advanced disease encompassing lymph node metastases in the mesenteric root, para‐aortic lymph node metastases, as well as liver metastases and peritoneal carcinomatosis. Palliative intervention in terms of superior mesenteric vein stenting or resection of central mesenteric metastases and/or percutaneous nephrostomy and J stent treatment was beneficial in the majority of the patients. They concluded by saying that extensive abdominal fibrosis associated with clinically significant symptoms of intestinal ischaemia and/or obstructive uropathy was linked to advanced disease in patients with SI NETs. Prompt recognition and minimally invasive intervention was effective in disease palliation.

Royal Free Hospital. In another fairly recent paper entitled “Neuroendocrine tumors and fibrosis: An unsolved mystery?”, published by Professor Martyn Caplin of the Royal Free (and others), where this issue is discussed alongside the role of serotonin, growth factors, and other peptides in the development of NET related fibrotic reactions.  They also suggested serotonin as the main culprit in both CHD fibrosis and in mesenteric/retroperitoneum and expressed many of the factors above.  This study suggested that up to 50% of SI NET patients may be involved but looking at both reports together indicates that the first study above only isolated clinically significant cases whereas Royal Free looked for signs in all cases.

Another recent paper (also a paid subscription) from Royal Free (Caplin et al) indicated that the severity of mesenteric desmoplasia did not seem to demonstrate a statistically significant effect on overall survival or long-term outcome (taken from a study of 147 patients at Royal Free London). Sounds like good news but there are clearly consequences that could arise from the issue.

I do not have access to all the texts above, only the abstracts which I’ve linked above (all only available from paid subscriptions).

One older publication authored by known UK NET expert endocrinologist, covered some of the above issues but added that fibrosis in the pleural/pulmonary areas and the skin could also be associated.   For ease of reference, the following extracts are cited to Fibrosis and carcinoid syndrome: from causation to future therapy Maralyn Druce, Andrea Rockall and Ashley B. Grossman Druce M. et al. Nat. Rev. Endocrinol. 5, 276–283 (2009); doi:10.1038/nrendo.2009.51

Mesenteric fibrosis and carcinoid syndrome.  Intestinal fibrosis in a series of 37 patients with jejunoileal carcinoid tumors, 8 of 12 patients with bowel obstructions had evidence of fibrosis or kinking of the bowel.6 among 36 patients with carcinoid syndrome who were seen at Yale university, 15 either had fibrosis at the time of surgery, or developed it subsequently. In a surgical series of 121 patients with midgut carcinoid tumors, 75 required laparotomy, due to abdominal pain; of these patients, 59 were noted to have marked mesenteric fibrosis at the time of surgery. Spread of the primary tumor into the mesentery and peritoneum can result in a marked fibrotic reaction. This fibrosis can mat together multiple loops of bowel and result in kinking, ischemia, volvulus and obstruction.

Retroperitoneal fibrosis. True retroperitoneal fibrosis is a rare clinical entity, in which inflammation results in fibrosis throughout the retroperitoneum. In two-thirds of patients this condition is idiopathic. The majority of cases that are not idiopathic are associated with drugs, such as antihypertensive agents and methysergide. Although retroperitoneal fibrosis is not commonly seen in the context of carcinoid syndrome and has not been reported in any recent, major review, several cases have been reported in literature. 

Pleural and Pulmonary Fibrosis. In a review of 50 patients with carcinoid tumors who presented to a single unit over 9 years and were examined using CT, 14 patients had pleural thickening, and in 9 of these cases no other attributable cause was established. All 14 patients had developed this pleural thickening within 2 years of being diagnosed as having carcinoid syndrome, and 7 of the 9 patients also had fibrosis elsewhere, for example, in the heart valves, skin or mesentery. Carcinoid syndrome has rarely been described as a cause of alveolar fibrosis, but fibrosis elsewhere in the lung occurs more frequently. in a series of 25 patients known to have peripheral carcinoid tumors of the lung, 19 displayed hyperplasia of neuroendocrine cells elsewhere in the lung, and 8 patients (25%) had lesions of obliterative bronchiolitis, including 2 with asymptomatic obstruction of airflow. These data suggest that bronchiolar fibrosis is not uncommon, although it is usually subclinical.

Skin fibrosis. Dermal fibrosis may be primary or secondary to peripheral vasospasm, which occurs in response to vasoconstrictor substances that are secreted by the tumor. Carcinoid syndrome associated with scleroderma has been reported: in one series, its prevalence was 2 cases in 25 individuals. This complication of carcinoid syndrome is usually a late feature and may be attenuated by the use of cyproheptadine hydrochloride, parachlor phenylalanine and prednisolone, which suggests a causative role for tryptophan metabolism and 5-HT”

What happened to me?

Since I was diagnosed in 2010, I’ve always known I’ve had a fibrosis issue in the retroperitoneal area, as it was actually identified on my very first CT Scan, which triggered my diagnosis.  Here’s how the radiologist described it – “There is a rind of abnormal tissue surrounding the aorta extending distally from below the renal vessels. This measures up to 15mm in thickness”.  He went on to describe that “almost certainly malignant”.  The second and third scans would go on to describe as “retroperitoneal fibrosis” and “a plaque like substance”.  Interestingly the fibrosis itself does not appear to ‘light up’ on nuclear scans indicating it was not cancerous (see below).

I really didn’t know what to make of this issue at diagnosis, although I did know the aorta was pretty important!  Fortunately I had a surgeon who had operated on many NET patients and has seen this issue before.  After my first surgery, he described it as a “dense fibrotic retroperitoneal reaction encircling his aorta and cava (inferior vena cava (IVC))”. My surgeon was known for difficult and extreme surgery, so as part of the removal of my primary, he also spent 3 hours dissecting out the retroperitoneal fibrosis surrounding these important blood vessels and managed 270 degree clearance. The remnant still shows on CT scans. Some of the removed tissue was tested and found to be benign, showing only florid inflammation and fibrosis (thankfully).  That said, the abstract papers above has led me to believe that my retroperitoneal fibrosis is clinically significant.

Routine surveillance in 2018 has picked up that retroperitoneal fibrosis is potentially impinging on important vessels in this area, particularly the left ureter but including some blood vessels. A follow up Ga68 PET confirms active lymph nodes in the retroperitoneal area that might be contributing to continued or new fibrosis growth.

In order to further assess risk to my kidneys, I had a different nuclear can known as a Renal MAG3. This scan looks at the blood supply, function and flow of urine from the kidneys. The output will inform my MDT and surgical team looking at treatment options to counter the risk of damage and the timing of potential surgery to correct the issue. I’m happy to report that the MAG3 scan confirmed there are no blockages to my kidneys or bladder. It did confirm my right kidney is doing 60% of the work, the suspected left one is covering the remaining 40% effort.  Apparently it’s pretty normal that it isn’t exactly 50/50.  Surgery is now on the back burner (phew!).  The kidney function will be monitored closely going forward.

Summary

These issues need to be identified early on in diagnostics, preventative treatment considered and then monitored going forward.  Potential complications may include (but not be limited to) bowel and blood vessel obstructions.  Retroperitoneal fibrosis also needs to be monitored as potential complications may include (but not be limited to) obstructive uropathy.

For those worried about this issue, please note that when you look at the statistics from Uppsala, only 4.5% of cases are classed as clinically significant and with the retroperitoneal area, the figure reduces to 2%.

Neuroendocrine Cancer is normally slow growing BUT …..

Thanks for reading