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Simple Summary: Serum TSH suppression in the management of PTC patients will inevitably cause iatrogenic thyrotoxicosis. Our study challenges, for the first time, the role of human recombinant thyrotropin (rh-TSH) as a mitogen on PTC cell lines. For this study, both K1 and TPC-1 cells were treated with clinically relevant rh-TSH under various conditions. The expression levels of TSHR and thyroglobulin (Tg) were determined and, subsequently, the proliferation and migration were assessed. Additionally, cells were engineered to overexpress TSHR in order to multiply TSH signal transduction. Under the conditions employed, rh-TSH was inadequate for inducing either the proliferation or the migration rate of both transformed and non-transformed cells, while Tg expression was increased. We report that, clinically speaking, rh-TSH doses cannot induce proliferation and migration in PTC cell lines, thus questioning TSH suppression in PTC patients. Further research is warranted to dissect the underlying mechanisms. These results could translate into better PTC patient management. Thyrotropin (TSH) suppression is required in the management of patients with papillary thyroid carcinoma (PTC) to improve their outcomes, inevitably causing iatrogenic thyrotoxicosis. Nevertheless, the evidence supporting this practice remains limited and weak, and in vitro studies examining the mitogenic effects of TSH in cancerous cells used supraphysiological doses of bovine TSH, which produced conflicting results. Our study explores, for the first time, the impact of human recombinant thyrotropin (rh-TSH) on human PTC cell lines (K1 and TPC-1) that were transformed to overexpress the thyrotropin receptor (TSHR). The cells were treated with escalating doses of rh-TSH under various conditions, such as the presence or absence of insulin. The expression levels of TSHR and thyroglobulin (Tg) were determined, and subsequently, the proliferation and migration of both transformed and non-transformed cells were assessed. Under the conditions employed, rh-TSH was not adequate to induce either the proliferation or the migration rate of the cells, while Tg expression was increased. Our experiments indicate that clinically relevant concentrations of rh-TSH cannot induce proliferation and migration in PTC cell lines, even after the overexpression of TSHR. Further research is warranted to dissect the underlying molecular mechanisms, and these results could translate into better management of treatment for PTC patients. [ABSTRACT FROM AUTHOR]