The utility of Ga-DOTATATE and F-FDG PET/CT in predicting the response to tyrosine kinase inhibitors in patients with advanced medullary thyroid cancer.

BACKGROUND

Tyrosine kinase inhibitors (TKIs) have significantly improved the prognosis of patients with advanced medullary thyroid cancer (MTC). However, treatment response heterogeneity leads to challenges in predicting individual favourable response. This study evaluated the correlation between PET metrics on Ga-DOTATATE and F-FDG PET/CTs prior to treatment, and TKI response.

METHODS

This study retrospectively evaluated patients with metastatic MTC who received TKIs at a tertiary care hospital and had prior Ga-DOTATATE and/or F-FDG PET/CT imaging. Patient demographics, treatment and PET/CT data were collected. Standardized Uptake Value (SUV) max, SUVmean, Total Lesion Activity (TLA) and Metabolic Tumor Volume (MTV) were determined per PET/CT.

RESULTS

In the 25 patients, mean age at diagnosis was 48 (±15) years; 11 (44%) were female and 21 tumors harbored RET driver alterations. Thirty-six TKI treatments were administered (11 patients received two TKIs sequentially). RECIST response rates (available in 32/36 treatments) included; stable disease in 8/32 (25%), partial response in 23/32 (72%) and complete response in 1/32 (3%) treatments. In total, 30 pre-TKI PET/CTs (24 Ga-DOTATATE PET/CTs, 6 F-FDG PET/CTs) were performed. Pre-TKI Ga-DOTATATE PET/CTs did not correlate with TKI treatment response. In the F-FDG cohort, high MTV and TLA correlated with a better structural response (p < 0.001) and high SUVmean correlated with a longer time to reach optimal response (p = 0.037).

CONCLUSIONS

In a small cohort of MTC patients, MTV and TLA on F-FDG PET/CT were associated with the structural response of TKI treatment, suggesting their potential utility in identifying patients who are likely to respond significantly. In contrast, TKI response showed no correlation with uptake on Ga-DOTATATE PET/CT.