Burden of metastatic bone disease measured on 18F-NaF PET/computed tomography studies as a prognostic indicator in patients with medullary thyroid cancer.

Purpose The aim of the study was to assess the association between the burden of metastatic bone disease measured on F-18-NaF PET/computed tomography (CT) studies and the overall survival (OS) of patients with medullary thyroid cancer (MTC). Methods We retrospectively analyzed 31 patients with MTC who performed 18F-NaF PET/CT studies to assess skeletal metastases. The outcomes of the patients (dead or alive) were established based on the last information available on their files. In the studies considered positives for skeletal metastases, the burden of metastatic bone disease was established calculating the fluoride tumor volume (FTV). The FTV was defined using isocontour thresholds based on percentages of maximal standardized uptake values (SUVmax) in the lesions. These percentages varied from lesion to lesion and were established by visual analysis. The patients were divided into three groups as follows: without skeletal metastases (n = 11), with low FTV (<= 50 cm(3); n = 11) and with high FTV (>50cm(3); n = 9). The Kaplan-Meier curves were used to analyze the OS in the three groups of patients and the log-rank test was used to determine the statistical significance of the difference between the groups. Results There were statistically significant differences in the OS between the group with high FTV and the groups of patients with low FTV (P = 0.036) and without skeletal metastases (P = 0.001). There was not a statistically significant difference between the groups of patients with low FTV and without skeletal metastases (P = 0.147). Conclusion In patients with MTC, the burden of metastatic bone disease is associated with OS.