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.

This diagram gives the common locations in Neuroendocrine Neoplasms (note that term includes NEC and NET).

Knowns and unknowns of bone metastases in patients with neuroendocrine neoplasms: A systematic review and meta-analysis (abstract only)

Garcia-Torralba, Esmeralda et al. Cancer Treatment Reviews, Volume 94, 102168 – click here or on the graphic below to read more – note only the abstract is available, the rest is unfortunately behind a paywall. The graphic is telling though (if accurate). Also worth noting that the title states “Neuroendocrine Neoplasms” so possibly include Neuroendocrine Carcinomas. If so, the data in the graphic is probably not a true reflection of well differentiated NETs. I’m hoping to get a full copy so I can ascertain how the data breaks down for NEC and NET separately.

This study from the UK – The Christie Manchester ENETS Centre of Excellence is good, looking at all Neuroendocrine Neoplasms – click here.

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. I attach the German study for small intestine NETs – click here.

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.

Resources:

1. Knowns and unknowns of bone metastases in patients with Neuroendocrine Neoplasms: A systematic review and meta-analysis. Garcia-Torralba, Esmeralda et al. Cancer Treatment Reviews, Volume 94, 102168 (abstract only)

2. Identification of Areas for Improvement in the Management of Bone Metastases in Patients with Neuroendocrine Neoplasms, Kok Haw Jonathan Lim; Hussain Raja; Paolo D’Arienzo; Jorge Barriuso; Mairéad G. McNamara; Richard A. Hubner; Wasat Mansoor; Juan W. Valle, Angela Lamarca Neuroendocrinology (2020) 110 (7-8): 688–696. https://doi.org/10.1159/000504256

3. Mathew A, Hauptmeier P, Schaarschmidt BM, Fendler WP, Führer D and Lahner H (2025) High incidence and poor prognosis of bone metastases in functioning small intestinal neuroendocrine tumors. Front. Endocrinol. 16:1680209. doi: 10.3389/fendo.2025.1680209

Thanks for reading.

Ronny