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QUESTION  I would be so grateful for your comments please –I am a 54 year old female who had a papillary carcinoma at age 16 which was treated with a  thyroidectomy and removal of positive lymph nodes in the neck initially. Since the first diagnosis I had two subsequent malignant nodules within a +- 5 year period  which were also surgically removed.  I then had two RAI treatments +- 25 years ago and was placed on 300 microgram of thyroxine daily (Eltroxin).

I have been monitored regularly by an oncologist and have also had regular mammograms. In 2010 I presented with a hormone positive, node negative Stage 1 invasive lobular breast carcinoma (not identified by a mammogram). I had a left mastectomy and after a low recurrence risk result from an Oncotype DX test,  I have been taking an aromatase inhibitor (Femara). I have had regular chest CT and breast MRI follow up and annual thyroid hormone tests. My thyroxine dose was reduced to 150 microgram/day as my oncologist said the thyroid function  was well suppressed and the high dose was of concern.

In mid December I had flu symptoms with a sore throat and cough and consulted my GP who identified a thyroid nodule. On an US it is described as:  “small amount of residual thyroid tissue present with a 7.8mm solid nodule. There is a small cystic component posteriorly, no associated calcification or hyperaemia within. There is a focus of calcification measuring 4mm in the right lobe, no solid or cystic nodules in the right lobe. There are some small left-sided cervical lymph nodes measuring 5-6mm in max diameter. Thyroid function test and isotope study recommended. I feel devastated by this development and have two questions – from everything I read a FNA should be done rather than an isotope study to check for malignancy?  Could the lowered thyroxine dose have stimulated the thyroid cancer to recur?  I have already resigned myself that more surgery will be necessary although it will depend on the oncologist consultation and FNA result. I pray for a worst case scenario of just a positive node with no mets.  Do you have any other comments that may be helpful to me?
RESPONSE  The question is : what was your serum thyroglobulin (Tg) on 300 of T4 and what was it on 150? Tg would have been suppressed on 300 and might not on 150.300 is a large dose but you had been on it for a long time with (?) no apparent ill effects.It is possible the reduced dose could have contributed to a recurrence but it is not a certainty. In manay women 150ug/day would be a suppressive dose.
You are correct that an FNA is the first investigation of choice and that, if positive for recurrence, surgery would be required.However, if there were to be any radioactive iodine uptake measurable in the neck (after an isotope scan) then there would be a possibility of giving radioiodine to wipe out remaining thyroid tissue. Hope this helps