micrometastasis (n.): the spread of cancer cells from the primary tumor to distant sites to form microscopic secondary tumors.
My post-RAI WBS turned up activity in my “residual thyroid tissue and/or local lymph nodes”. (great specificity nuc med) The residual thyroid tissue is expected to show up because your thyroid is literally attached to most of the structures in your neck (most notably your windpipe) so they can’t physically get EVERY cell without damaging other, more important organs. The part about them not knowing if it was also showing uptake in local lymph nodes makes me entirely not confident in the nuc med physicians at my hospital. Well that and the fact that they didn’t think I needed a post-RAI WBS when it is ALWAYS done everywhere else… but I digress…
The WBS also showed “diffuse uptake in the left lung posteriorly” in a pattern “not consistent with focal metastatic disease.” What this means is there was RAI uptake in my lung but it didn’t show focal tumors (macrometastasis). If you remember, radioactive iodine is ONLY taken up by thyroid cells in the body (cancerous or regular) and whatever they gave me that wasn’t taken up by my residual thyroid tissue was excreted in urine, sweat, and saliva. There is NO reason there should have been any uptake in the lung with the exceptions of the presence of thyroid cells in the lung tissue OR an infection/inflammatory process (like pneumonia or pleural effusion). The recommendation by nuc med was to get a chest x-ray for further characterization which I had done on Friday. My chest x-ray was CLEAR. Meaning I have no pneumonia or pleural effusion or any other inflammatory process.
So what does this mean? Without the presence of focal metastatic disease (cancerous nodules) there is the strong possibility that I have diffuse micrometastasis of my cancer throughout my left lung. It could also have been a fluke in the machine but that is the less likely scenario.
So ok, what does that mean? In patients without metastatic disease elsewhere (this is why the lymph node comment bothers me) long term survival rates are very high when lung mets are too small to see on x-ray and have only shown up on post-treatment WBS. 10-year rates are still near 100% with these diffuse micrometastases… but when the mets become micronodules (<1cm) survival rates drop to around 40% and when mets become macronodules (>1cm) rates drop to 15%. It not showing on the x-ray is common in patients my age and is actually a good thing. Also, the dose of RAI I had (200mCi) is exactly what would have been prescribed had we known about this prior to my treatment and the follow-up course should not change at this point. In 8-12 months I should have a follow-up scan and if uptake is present on that scan, I will need another 200mCi of RAI, repeat that cycle until no uptake is seen on the post scans. We should also be monitoring my thyroglobulin levels and if they are elevated that will indicate persistent disease.
That all being said, I think its time for a second look/opinion on my case. I plan on calling my PCP for a referral to a thyroidologist and the only ones in state are at U of M. Any metastasis in thyroid cancer tends to mean higher chances of recurrence and/or further spread so I think having a specialist review my case would be a good thing at this point and if they have a more aggressive treatment plan in mind I will probably transfer my care to them.
So lots to think about, pray about, and try not to worry about in the coming months!