Basic research
Does L-thyroxine treatment downregulate EGF receptor expression in endemic non-toxic nodular goitre?

Introduction: TSH receptor (TSH-R) is mainly expressed in thyroid follicular cells (TFC), regulating thyroid growth. Epidermal growth factor receptor (EGF-R) is often found upregulated in many human tumours. CD44 has been found to be implicated in thyroid tumour formation, carcinogenesis included, and has been selected in our study as a “negative” control for TSH-R and EGF-R, because no evidence exists for its regulatory effects on thyroid growth processes during L-thyroxine treatment.

Material and methods: Fine-needle aspiration biopsies of the thyroid gland were performed in 18 adult patients with endemic non-toxic nodular goitre (NTNG) before and during L-thyroxine treatment (either 50 or 100 µg/daily, depending on goitre volume and patient age) after 6 and/or 12 months, and TSH-R, EGF-R and CD44 expressions were assessed immunocytochemically in TFC.

Results: Before L-thyroxine treatment – positive immunoreactivity for EGF-R [EGF-R (+)], TSH-R [TSH-R (+)] and CD44 [CD44 (+)] was observed in 61, 72 and 82% of NTNG cases, respectively. During L-thyroxine therapy – out of 5 original EGF-R (+) and out of 4 original immunonegative [EGF-R (–)] cases, all were found EGF-R (–); out of the original 7 TSH-R (+) cases, 86% became TSH-R (–), but 2 TSH-R (–) cases became TSH-R (+); out of 7 CD44 (+) cases, 71% remained CD44 (+).

Conclusions: EGF-R expression is completely downregulated in the course of L-thyroxine treatment of endemic nodular goitre, the mechanism which could be considered as being involved in goitre involution.