Larotrectinib-Enhanced Radioactive Iodine Uptake in Advanced Thyroid Cancer

This correspondence reports a case of advanced papillary thyroid cancer with lung metastases, where the NTRK inhibitor larotrectinib restored radioactive iodine (RAI) uptake after prior treatment failure. A 64 year old patient with an EML4-NTRK3 fusion gene showed no RAI uptake during lenvatinib therapy but exhibited significant uptake three weeks after starting larotrectinib. The findings suggest that larotrectinib may reverse RAI refractoriness by inhibiting oncogenic signaling pathways, similar to MAPK inhibitors. While the patient achieved a partial response with larotrectinib alone, the case highlights the potential for RAI retreatment in such scenarios. The study underscores the need for further research on NTRK inhibitors in thyroid cancer redifferentiation strategies.

This correspondence reports a case of advanced papillary thyroid cancer with lung metastases, where the NTRK inhibitor larotrectinib restored radioactive iodine (RAI) uptake after prior treatment failure. A 64 year old patient with an EML4-NTRK3 fusion gene showed no RAI uptake during lenvatinib therapy but exhibited significant uptake three weeks after starting larotrectinib. The findings suggest that larotrectinib may reverse RAI refractoriness by inhibiting oncogenic signaling pathways, similar to MAPK inhibitors. While the patient achieved a partial response with larotrectinib alone, the case highlights the potential for RAI retreatment in such scenarios. The study underscores the need for further research on NTRK inhibitors in thyroid cancer redifferentiation strategies.