Novel concepts for initiating multitargeted kinase inhibitors in radioactive iodine refractory differentiated thyroid cancer.

Multitargeted kinase inhibitors have been shown to improve progression-free survival in patients with structurally progressive, radioactive iodine refractory differentiated thyroid cancer. While the inclusion criteria for phase 3 clinical trials and clinical practice guidelines provide guidance with regard to the minimal requirements that need to be met prior to initiation of a multitargeted kinase inhibitor, a better way to integrate the rate of structural disease progression with the size of the metastatic foci to more precisely define the optimal time to recommend initiation of therapy for individual patients is needed. In this manuscript we describe how to use assessments of tumor size and growth rates (structural disease doubling times) to define the critical point in time when the volume and rate of progression of metastatic structural disease merits consideration for initiation of systemic therapy (the inflection point).