Bone metastases in Neuroendocrine Tumours (NET)

Bone metastases in Neuroendocrine Tumours (NET)

Many of you will know that I am a stage IV small intestine NET and I have one bone metastasis (BM) reported. The initial evidence of this BM came from my very first Ga68 PET scan. It said “there is intense focal uptake of tracer in the right 11th rib”. This rib is at the bottom of the ribcage at the back of the body. Along with rib 12, they’re called ‘floating ribs’ as only one end is joined to another part of the cage. The closest organs to this rib is the posterior liver and right kidney. I have no symptoms and a follow up Ga68 PET conducted in 2021 confirmed it was ‘stable’. This follow up PET also noted very faint activity in the right sacrum (an observation).

Initially I was sceptical given the false positives that can happen with somatostatin receptor PET, particularly in bones. But my report specifically excludes them from anything listed as physiologic uptake. I have accepted its existence and membership of the bone met club. At least I know the source of my 3 fractured ribs on the left ……. I fell off my bike!

Tumours reach bones mainly through metastasis, where cancer cells break away from the primary tumour, travel via the bloodstream or lymphatic system, and lodge in bone tissue. Once there, they disrupt the normal balance of bone-building (osteoblasts) and bone-resorbing (osteoclasts) cells, leading to either bone destruction (lytic lesions) or abnormal bone growth (blastic lesions). In cancer generally, the most common primary sources for BM are breast cancer, kidney cancer, lung cancer, prostate cancer, thyroid cancer. However, in NETs, these locations in general cancer terms (less lung) are uncommon as a primary location. In NETs, BM are less common than liver metastases and normally only show alongside liver metastases. They are most common in Pancreatic, small intestine and lung NETs and rarely in others. Unknown primary features but pancreatic or small intestine origins are often suspected.

I was therefore interested when a NET specialist I follow posted a tweet about BM in advanced small intestine NETs, including a link to a German study. The statistics are interesting. BM are common in patients with well differentiated NETs. Dr Thor also points out the utility behind the routine use of SSTR PET imaging. This has led to diagnosis of many more patients with BM (and that seems to fit my profile and the timing). The German study shows that BM are detected in 1/3 of small intestine NETs and more commonly seen among those with functional NETs. The aforementioned study did point out similar statistics in pancreatic NETs. Dr Thor said he had not seen a reason to routinely offer antiresorptive therapy but would recommend in patients with extensive BM, adding that it is time for a prospective study, echoing similar calls in the other studies. A prospective study is a type of research that follows participants forward in time, observing outcomes as they occur. This is a long term study following patients and can help discover cause and effect relationships. It can also help estimate relative risk of disease based on exposure, allows study of multiple outcomes simultaneously and it can help reduce bias.

For those who want to read more, I attach the German study mentioned above – click here.

This study from the UK – The Christie Manchester ENETS Centre of Excellence is also good, looking at more than just small intestine NETs – sorry I need to link to X (formerly twitter) for this one – click here. (Abstract only)

If you want to know more about NET and BM, let me know which area of diagnosis and treatment and I’ll research and add here.

In the meantime, I’ll continue to watch out for any symptoms of my single and asymptomatic bone metastasis. I guess the key symptom is pain and I’m not seeing any of that.

thanks for reading

Ronny