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Introduction Therapy for hypothyroid obese patients is still under definition since the thyrotropin‐stimulating hormone (TSH) level is a less reliable marker of euthyroidism than nonobese patients. Indeed, TSH levels positively correlate with body mass index (BMI), and this increase may be a compensatory mechanism aimed at increasing energy expenditure in obese people. In contrast, the correlation of BMI with thyroid hormone levels is not completely clear, and conflicting results have been obtained by several studies. The L‐T4 replacement dose is more variable in obese hypothyroid patients than in nonobese patients, and a recent study indicated that the L‐T4 replacement dose is related to lean body mass in obese thyroidectomized patients. We aimed to study the correlations of L‐T4‐administered dose, thyroid hormone levels and TSH secretion with basal metabolic rate (BMR) and total calculated deiodinase activity (GD) in obese and nonobese athyreotic patients. We also looked for individualized L‐T4 replacement dose set points to be used in clinical practice. Methods We studied retrospectively 160 athyreotic patients, 120 nonobese and 40 obese. GD was calculated by SPINA Thyr 4.2, the responsiveness of the hypothalamic/pituitary thyrotrope by Jostel's thyrotropin (TSH) index and BMR by the Mifflin‐St. Jeor formula, the interplay of GD and BMR with L‐T4, thyroid hormones and TSH index (TSHI) was also evaluated. Results In our study, the L‐T4 dose was an independent predictor of GD, and approximately 30% of athyreotic patients under L‐T4 therapy had a reduced GD; FT4 levels were higher and negatively modulated by BMR in obese athyreotic patients respect to nonobese, in these patients a T4 to T3 shunt, in terms of TSHI suppression is observed suggesting a defective hypothalamic pituitary T4 to T3 conversion and a resistance to L‐T4 replacement therapy. Conclusions L‐t4 dose is the most important predictor of GD, BMR modulates T4 levels in obese athyreotic patients that are resistant to L‐T4 replacement therapy.

The receptor for advanced glycation end products (RAGE) is implicated in diabetes and obesity complications, as well as in breast cancer (BC). Herein, we evaluated whether RAGE contributes to the oncogenic actions of Insulin, which plays a key role in BC progression particularly in obese and diabetic patients. Analysis of the publicly available METABRIC study, which collects gene expression and clinical data from a large cohort (n = 1904) of BC patients, revealed that RAGE and the Insulin Receptor (IR) are co-expressed and associated with negative prognostic parameters. In MCF-7, ZR75 and 4T1 BC cells, as well as in patient-derived Cancer-Associated Fibroblasts, the pharmacological inhibition of RAGE as well as its genetic depletion interfered with Insulin-induced activation of the oncogenic pathway IR/IRS1/AKT/CD1. Mechanistically, IR and RAGE directly interacted upon Insulin stimulation, as shown by in situ proximity ligation assays and coimmunoprecipitation studies. Of note, RAGE inhibition halted the activation of both IR and insulin like growth factor 1 receptor (IGF-1R), as demonstrated in MCF-7 cells KO for the IR and the IGF-1R gene via CRISPR-cas9 technology. An unbiased label-free proteomic analysis uncovered proteins and predicted pathways affected by RAGE inhibition in Insulin-stimulated BC cells. Biologically, RAGE inhibition reduced cell proliferation, migration, and patient-derived mammosphere formation triggered by Insulin. In vivo, the pharmacological inhibition of RAGE halted Insulin-induced tumor growth, without affecting blood glucose homeostasis. Together, our findings suggest that targeting RAGE may represent an appealing opportunity to blunt Insulin-induced oncogenic signaling in BC.