PET-CT for — Rare and Unusual Cancers

It depends on whether your specific tumour type absorbs FDG, the standard tracer. Many rare cancers — including most sarcomas, high-grade neuroendocrine tumours, and Merkel cell carcinoma — are reliably PET-avid. Others, such as prostate cancer, most kidney cancers, and low-grade NETs, do not absorb FDG well and may appear normal on a standard scan even when disease is active. Ask your oncologist specifically whether FDG is appropriate for your cancer type before the scan is arranged, rather than assuming any PET-CT will give a reliable picture.

Gallium-68 DOTATATE PET uses a tracer that binds to somatostatin receptors on neuroendocrine tumour cells, rather than detecting glucose uptake. Because most low-grade NETs are slow-growing and use little glucose, FDG often misses them entirely — Gallium DOTATATE finds them with much greater sensitivity. NCCN and ESMO guidelines recommend it as the preferred scan for low-grade and intermediate-grade NETs. If you have been diagnosed with a NET and have only had FDG PET, ask your oncologist whether Gallium DOTATATE was considered and, if not, why.

Ask why rather than assuming something has been missed. For some rare cancers, CT or MRI gives better information than any available PET tracer. For others, staging has already been established and a PET scan would not change what happens next. The useful question is: is there any PET tracer that would add meaningful information for my specific cancer type, and if so, has it been considered? A team that cannot say what clinical question the scan would answer is worth pressing on that point.

PET-CT is one of the recommended investigations when a cancer of unknown primary is suspected. It can sometimes reveal a primary tumour that CT or MRI alone did not show, and identifying the origin can change the treatment approach. It does not always succeed — a proportion of unknown primary cancers remain unexplained even after thorough imaging. NCCN includes PET-CT in the CUP work-up for selected presentations. If you have been told your cancer is of unknown primary and PET-CT has not been discussed, ask whether it is appropriate.

For standard FDG PET-CT, plan to be at the imaging centre for around two hours. Most of that time is a waiting period after the tracer injection while it distributes through your body. The scan itself takes roughly thirty minutes and is not painful — you lie still on a table that moves through the scanner. You will be asked to fast for several hours beforehand and to avoid strenuous exercise the day before. For specialised tracers, timing and preparation differ, and the imaging centre will give you written instructions when the appointment is confirmed.

CION does not run its own scanners — PET imaging is arranged through partner imaging centres. When a specialised tracer is clinically indicated for your cancer type, your CION oncologist will coordinate the referral to an appropriate facility. Not every tracer is available at every centre, so the appointment may be at a different location than a standard FDG scan would be. Ask your treating oncologist which tracer has been requested, where the scan will take place, and what prior records or paperwork the imaging centre will need from you.