Hyperfunctioning thyroid cancers are rare. Current ATA guidelines recommend against routine biopsies of autonomous thyroid nodules (ATNs)(1). We present two cases of thyroid cancer found in autonomous nodules.
Case 1
A 30-year-old female with subclinical hyperthyroidism was referred for pre-pregnancy planning. Thyroid ultrasound showed two sub-centimetre TIRAD 4 nodules arising in the upper poles bilaterally. Technetium scan showed increased uptake in both nodules. The ultrasound also showed an abnormal right-sided level 3 lymph node. Biopsy of the right upper pole nodule and the lymph node showed papillary thyroid carcinoma with lymph node metastasis. The patient underwent total thyroidectomy and lymph node excision. Final histology showed lympho-vascular infiltration and BRAF positivity. She underwent radioiodine ablation.
Case 2
A 72-year-old female with minimal thyrotoxic symptoms, was found to have suppressed TSH, free T4 25.2pmol/L, free T3 of 7.5pmol/L, and TRAb 4.5U/L. Thyroid ultrasound showed multinodular goitre with a suspicious left upper pole nodule, which appeared irregular, hypoechoic with poor infiltrated margins. Technetium scan suggested that this nodule was autonomous. Subsequent biopsy confirmed papillary thyroid cancer. She underwent total thyroidectomy. Final histology showed a well capsulated intrathyroidal papillary thyroid cancer of 7 mm without lymph node involvement, or vascular invasion. She did not receive radioiodine ablation.
Discussion
Thyroid cancer is not thought to be common in ATNs. There are approximately 60 case reports of thyroid malignancy within ATNs. Current literature suggests the rate of malignancy within ATNs is less than 10%. Low TSH may be protective, and autonomous thyroid cancer cells are usually well differentiated and less likely to metastasise(2).
Conclusion
The vast majority of ATNs are benign. However careful assessment with thyroid ultrasound may identify rare cases of hyperfunctioning thyroid malignancy.