[ 18 F]FDG PET/CT can trigger relevant oncological management changes leading to favorable outcome in iodine-negative thyroid cancer patients.

BACKGROUND: In patients with iodine-negative thyroid cancer (TC), current guidelines endorse an [18 F]FDG PET/CT to identify dedifferentiated sites of disease. We aimed to determine the rate of oncological management changes triggered by such a molecular imaging approach, along with the impact on outcome.

METHODS: 42 consecutive patients with negative findings on [131 I] whole body scan were scheduled for [18 F]FDG PET/CT and treatment based on PET results were initiated. To determine the impact on oncological management, we compared the therapeutic plan prior to and after molecular imaging. Based on imaging follow-up, the rate of controlled disease (CD, defined as stable disease, complete or partial response) was also recorded, thereby allowing to assess whether [18 F]FDG-triggered management changes can also lead to favorable outcome.

RESULTS: We observed no alterations of the treatment plan in 9/42 (21.4%) subjects (active surveillance in 9/9 [100%]). Oncological management was changed in the remaining 33/42 (78.6%; systemic treatment in 9/33 [27.3%] and non-systemic treatment in 24/33 [72.7%]). Among patients receiving non-systemic therapy, the following changes were noted: surgery in 20/24 (83.3%) and radiation therapy in 4/24 (16.7%). In the systemic group, tyrosine kinase inhibitor (TKI) was prescribed in 8/9 (88.9%), while radioiodine therapy based on a TKI-mediated redifferentiation approach was conducted in 1/9 (11.1%). In 26 subjects with available follow-up, rate of CD was 22/26 (84.6%) and among those, 15/22 (68.1%) had experienced previous management changes based on PET/CT findings.

CONCLUSIONS: In subjects with iodine-negative TC, [18 F]FDG PET/CT triggered relevant management changes along with disease control in the vast majority of patients. As such, in dedifferentiated TC, [18 F]FDG PET/CT may serve as a relevant management tool and therapeutic decision-aid in the clinic.