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Background: BRAF and MEK inhibitors are cornerstones of the redifferentiation strategy in metastatic radioactive iodine (RAI)-resistant mutant thyroid cancers. We explored the exposure-toxicity relationship for dose-limiting toxicity (DLT) onset in patients treated with dabrafenib and/or trametinib and investigated whether plasma exposure was associated with RAI reuptake. Methods: We conducted a retrospective monocentric study in which we reviewed the electronic medical records of patients treated in our institution with a tumor redifferentiation strategy, for whom plasma concentration of dabrafenib, its active metabolite hydroxy-dabrafenib, and trametinib was measured. Trough concentrations (C minpred ) and total plasma drug exposure (area under the curve, AUC) of dabrafenib (AUC DAB ), hydroxy-dabrafenib (AUC OHD ), and trametinib (AUC TRA ) were estimated. Results: Of the 22 patients treated in a redifferentiation strategy between March 2014 and December 2021, 15 were included in this study. A dabrafenib- or trametinib-related DLT was experienced by 8 (62%) and 9 (64%) patients, respectively. Patients who experienced a trametinib-related DLT exhibited a significantly higher last AUC TRA than the average AUC TRA of patients who had no DLT (390, IQR: 67 vs. 215, IQR: 91 ng/mL·h -1 , respectively; p  = 0.008). Patients who experienced a dabrafenib-related DLT had a higher AUC DAB than observed in other patients (9265 ng/mL·h -1 vs. 6953 ng/mL·h -1 , respectively; p  = 0.09). No clinical and demographical characteristic was associated with the DLT onset. Overall, 9 of 15 (60%) patients demonstrated tumor redifferentiation. Patients in whom RAI reuptake was achieved had significant lower AUC DAB (6990 ng/mL·h -1 vs. 9764 ng/mL·h -1 , p  = 0.014; respectively) compared with patients who did not. Moreover, the relative exposure ratio of AUC OHD/DAB was significantly higher in patients who achieved RAI reuptake (1.11 vs. 0.71, respectively; p  = 0.0047). Conclusions: Our data suggest a relationship between DLT onset and trametinib plasma exposure, as well as an association between achievement of RAI reuptake and dabrafenib plasma exposure (AUC and ratio of AUC OHD/DAB ). These data imply that the use of plasma drug monitoring could be helpful in guiding clinical practice in redifferentiation treatment.

Metastatic thyroid cancers may dedifferentiate and become radioactive-iodine (RAI) resistant. A redifferentiating effect can be observed with inhibitors of the mitogen-activated protein kinase pathway in thyroid cancers with point mutation in oncogenes. This effect allows RAI reuptake that may lead to a therapeutic effect different from the antitumoral effect of the inhibitor. The potential redifferentiating effect of inhibitors targeting oncogenic fusion-genes was suggested by one adult and one pediatric patient using larotrectinib in NTRK -rearranged tumors. We report on three consecutive adult patients with metastatic RAI-resistant NTRK- rearranged thyroid cancer who received larotrectinib for disease progression and for whom the redifferentiating effect was examined. Larotrectinib-induced RAI reuptake in all or part of the metastatic disease for two patients and no reuptake was noted for the other patient. We demonstrate that redifferentiation of NTRK -rearranged RAI-resistant thyroid cancer with larotrectinib may exist but does not occur in all patients.

Background: Rates of adverse events with sorafenib were higher in the DECISION trial in radioactive iodine-refractory, advanced differentiated thyroid cancer (DTC) than in trials of sorafenib for other tumor types. One possible explanation is that sarcopenia, a known predictive factor of toxicity in patients with cancer, is more common in patients with DTC due to hormone suppressive therapy. Methods: This retrospective exploratory analysis was performed to assess whether the risk of early toxicity leading to dose modification (DMT) with sorafenib was higher in patients with sarcopenia compared with those without sarcopenia. The data set comprised patients from the phase III DECISION trial with a computed tomography scan available to determine muscle mass. The skeletal muscle (SM) cross-sectional area was used to determine the SM index and define sarcopenia. The end points were changes in body composition, DMT, early DMT (within 1 month), severe toxic events (STEs), and early STEs. Results: Overall, 365 patients were eligible for this analysis; baseline characteristics were well balanced between patients receiving sorafenib ( n  = 180) versus placebo ( n  = 185). Using a sarcopenia definition of an SM index less than the median sex-specific SM index, approximately half of the patients receiving sorafenib were at risk of sarcopenia (89/180; 49.4%), with wide geographical variation. At 6 months, the mean weight, body mass index, and lean body mass of patients receiving sorafenib were lower than at baseline and significantly lower than for patients receiving placebo (all p  < 0.0001). Most DMTs and STEs occurred in the first month of treatment. There was a nonsignificant trend for more early DMTs in patients with sarcopenia compared with those without sarcopenia (55.3% vs. 44.7%, respectively; p  = 0.2273). Conclusions: These results show a significant effect of sorafenib on muscle mass. However, there was no association between sarcopenia and DMT or early DMT, in contrast to observations in hepatocellular and renal cell carcinoma.

Background: In the Study of (E7080) Lenvatinib in Differentiated Cancer of the Thyroid (SELECT) phase 3 trial on advanced radioactive iodine-refractory differentiated thyroid cancer (rDTC), lenvatinib improved median progression-free survival over placebo by almost 15 months and induces an objective response rate of 64.8%, but adverse events occurred in almost all patients. The present study evaluates the efficacy and toxicity of lenvatinib treatment in real-life practice. Methods: Clinical charts of 88 consecutive patients treated with lenvatinib from July 2015 to June 2016 in 27 French centers were retrospectively reviewed. Patients treated for other thyroid cancer types ( n  = 11) or previously treated with lenvatinib within a trial ( n  = 2) were excluded and the remaining 75 rDTC patients formed the basis of this report. Results: 75 rDTC patients were analyzed (33 females, median age 65 years [range, 35-88 years]), 12 had an Eastern Cooperative Oncology Group performance status ≥2; 24 cases received lenvatinib as first line systemic treatment; 47 (63%) patients had documented progressive disease prior to treatment initiation. Distant metastases were located in lungs, bones, and lymph nodes (89%, 60%, and 69%, respectively). The initial treatment dose was 24 mg in 54 patients and was lower in the other 21 patients. The median follow-up was 7 months, with a median duration of treatment of 6 months [0.3-15]. Median progression-free survival was 10 months. Among the 65 patients with evaluation of tumor response during treatment, best tumor response was a partial response in 23 patients (31%) and stable disease in 38 (51%). Eleven patients (14.7%) discontinued lenvatinib because of disease progression. Forty-four (59%) and 23 (31%) patients had dose reductions or an interruption of lenvatinib for adverse events (AEs). The most frequent AEs related to treatment were fatigue, hypertension, weight loss, diarrhea, and anorexia. Eleven deaths occurred during the study (one considered to be drug related). Pneumothorax occurred in 2 patients with lung metastases. Conclusions: Real-life patients with rDTC can benefit from lenvatinib treatment. AEs are frequent and should be closely monitored.