Sutent and Thyroid

[Robbie2]

Dear Dr. Lupo,  You might not know the answer to this question, but I wrote you a month ago and told you about my kidney cancer medicine wreaking havoc on my thyroid. (Sutent) I started with a TSH of 100 June 28th, low free T4.  July 16th TSH was a 9.  July 24th TSH was a  5. (at that time I had been taking Thytrophin for 10 days)  When I started back on the medicine I had it rechecked two weeks later.  It was a 29, free T-4 was just a pinch over the normal range.  My Onc. did not want to increase the synthroid because the T-4 was a little high. One week later, still on the cancer med.  My TSH was a 13 and the free T-4 was a 1 which he said once again was fine.  my hair which I cut down to 1/4 inch has grown slightly.  However it keeps dropping (thinning)  I am perplexed why my free T-4 would be ok and my TSH is all over the map.  I am due for scans the end of October.  I usually have the bone and the ct scan the same day.  Could the contrast dye be effecting my hair and the thyroid.  The only time they checked my free T-3 was in July and it was normal.  Could you talk about the wacked TSH, normal free T-4. I trust my onc. about the cancer but not on the thyroid.  I wonder if i should see an endo. I started Synthroid June 29th, 0.5mg.  No dose increase since.  

[Mark Lupo, M.D.]

We are still learning about the abnormal thyroid function labs caused by Sutent.  There may be something to it that causes the T4 to appear elevated at times despite the high TSH and hypothyroidism.  The contrast may be further confounding the situation.  Next week is our annual thyroid association meeting and I believe there is some research to be presented on Sutent -- will let you know.

[Mark Lupo, M.D.]

If you are cycling on/off Sutent (as most do) the TSH will fluctuate as the effect of Sutent is to block iodine uptake but this effect appears to wear off when the medication is withdrawn.  That is perhaps why the TSH increase looks out of proportion to T4 decrease as TSH will move much more quickly than T4.  Will look for more info on this at the meeting.

[Robbie2]

Thank you, for looking into this.  Sutent has only been approved for a year and a half.  It is for RCC but is a crossover drug, in clinical stage three trials for many other cancers.  I imagine this will come up again as it becomes approved for other cancers.  I look forward to any insight uou could suggect to counter act the  effects of Sutent in my thyroid.  

[Robbie2]

Did you gain any useful insight about sutent and treating the resulting hypothyroidism.  

[Mark Lupo, M.D.]

Not really, there are other meds like sutent (tyrosine kinase inhibitors) that also effect thyroid function even in patients with thyroid cancer who have had their thyroid removed, it appears to increase levothyroxine requirements.  So, there is more than one mechanism of action in which it alters thyroid status.  The effect with sutent does not appear to be permanent and trying to keep up with thyroid status while cycling on/off the medication is the best advice at this point.