Radioiodine - do I have unusual resistance?

I've decided to try to understand my situation better before my next appointment with my oncologist.

I had a total thyroidectomy for papillary thyroid cancer in 2013, a lump in my right thyroid lobe, followed by 1.1GBq radioiodine ablation shortly after.

Six months later I had a follow up ultrasound which showed a 5x5x8mm lump left in my left thyroid bed. A whole body scan following this showed it took up radioiodine, so I had a second treatment dose of radioiodine - 5GBq.

Six months after that another follow up ultrasound showed the lump was still there, very slightly shrunk at 5x5x7mm.

Due to a few issues - miscommunication, changing consultants, plus me not pushing because I don't want further radioiodine treatment - I was told it would probably shrink to nothing over several more months and it was left at that, around last April.

During a follow up appointment earlier this year this was looked at again and it was decided I should have a whole body scan to follow this up and to check that nothing in my neck would take up radioiodine. I had a scan and the lump was still there and it took up radioiodine again. An ultrasound followed and confirmed the lump was still there in my left thyroid bed, still the same size as last year, 5x5x7mm.

I would like to know what this lump is. The thyroid cancer was in the right lobe, but this lump is in my left thyroid bed. Why would thyroid tissue survive so much radioiodine? Could it be normal thyroid tissue? It's still taking up radioiodine because it shows up on the whole body scans, but treatment doses haven't got rid of it.

My thyroglobulin levels are undetectable, my tgAb levels are either undetectable, or present but slowly decreasing, depending on who has tested it. I have been given different tgAb results.

Can anyone help?

Thank you.

[Clutter]

Cloud22,

As the lump is in the thyroid bed and taking up iodine it must be thyroid cells. It appears that you are either resistant to iodine-33 or insufficient dose is being given. Is the lump too small to remove surgically before another dose of RAI?

[Hidden in reply to Clutter]

I don't know about surgery, it hasn't been mentioned so I assume it's too small.

I know they give you iodine 131 for both the whole body scans and the treatment doses, so I can't understand why the treatment doesn't work if it's taking up the iodine for the scans.

Is it possible for thyroid cells to take up radioactive iodine but not get destroyed by it? I would have thought it would work just because I thought any radiation exposure would damage cells.

[Clutter in reply to Hidden]

Cloud22,

I had high dose 3700 MBq (100 mCi) because I had Hurthle Cell cancer which is more aggressive than Papillary. There were some thyroid hotspots showing on the whole body scan when I was discharged but there was none at the follow up lower dose whole body scan 5 months later. I can't work out how my dose compares with yours. I know much lower doses are sometimes prescribed and may not always be as efficacious as high dose.

You do appear to be taking up RAI although it is not destroying the cells. I was told that as long as thyroglobulin remained <6.0 there was little chance of recurrence.

For RAI refractory cancers radio beam therapy may be used.

[Hidden in reply to Clutter]

Hi Clutter, I think 3700MBq is 3.7GBq. So my first dose was a low dose, 1.1GBq, then my second was higher, 5GBq. My consultant said they went for 5 instead of 3 to make sure it got rid of all of it but it doesn't seem to have worked.

I have tried to do some research about RAI refractory cancers but I don't understand if they would still take up RAI and show up on a whole body scan? My assumption was that they no longer responded to iodine, do not take up iodine and therefore RAI treatment is ineffective for them.

I also still don't know if the lump is cancerous or benign, all I've been told when I've asked is 'we don't know'.

[Clutter in reply to Hidden]

Cloud22,

I'm sorry I don't have answers for you. I can only suggest you keep asking your consultant and/or oncologist what is happening. I hope it turns out that lump is benign.

[Hidden in reply to Clutter]

Yes me too. I will keep asking questions, hopefully I will get some answers when I see my consultant in a couple of weeks.