The gallium-68 dodecane tetraacetic acid tyr3-octreotate positron emission tomography (68Ga-DOTATATE-PET), also called 68Ga labeled equivalent radiopharmaceutical, could be the preferred diagnostic tool for recurrent or persistent medullary thyroid carcinoma (MTC), as published in The American Journal of Surgery.

The systematic review conducted by Pajak and colleagues included 5 articles ranging from 2009 to 2020 that compared 68Ga-DOTATATE-PET vs fluorine-18-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) scans for detecting recurrency in MTC after surgical excision.

All publications reported the sensitivity per patient for both diagnostic imaging tools. The results display a marked heterogeneity, with the sensibility of 68Ga-DOTATATE-PET ranging from 33.3% to 75.6%; regardless, all publications except 1 found this method to be superior to 18F-FDG-PET.


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Regarding the ability to detect lesions according to the location, 68Ga-DOTATATE-PET was better at detecting bone and lymph node metastasis vs 18F-FDG-PET with rates of 100% vs 46.3% and 92.8 vs 58.8%, respectively. In patients with hepatic metastasis, the studies are inconclusive since some claimed 68Ga-DOTATATE-PET performed better, but another study found that this imaging missed multiple lesions in the liver of a patient that only 18F-FDG-PET detected. The authors hypothesized that this phenomenon could occur due to a lower lesion-to-background ratio in hepatic tissue.

Above normal calcitonin levels are common in MTC, and its increase seems to correlate with better performance of both imaging tools. 68Ga-DOTATATE-PET showed higher sensitivity at levels of 500 pg/ml, whereas the same improvement occurred with levels higher than 1000 pg/ml for 18F-FDG-PET. Carcinoembryonic antigen (CEA) was used as a disease progression marker, and its higher levels in the blood also seem to improve the sensitivity of both imaging systems.

Regardless of the promising results of 68Ga-DOTATATE-PET for patients with MTC, its role has not yet been completely defined, and all of the publications included in the review analyzed a rather small sample. The reason for this could be the high costs of this study, which requires advanced infrastructure and makes it rarely available, the authors said.

“When compared directly to 18F-FDG-PET, there was a general trend in favor of 68Ga-DOTATATE-PET, though the observed difference was not significant,” the researchers said. “More research needs to be carried out before the specific role of this imaging can be better defined; however, 68Ga-DOTATATE-PET does appear to have an important role in the assessment of MTC patients in whom recurrence or metastasis are suspected by rising calcitonin or CEA, and/or imaging consistent with metastatic disease.”

Reference

Pajak C, Cadili L, Nabata K, Wiseman S. 68Ga-DOTATATE-PET shows promise for diagnosis of recurrent or persistent medullary thyroid cancer: a systematic review. The American Journal of Surgery. Published online March 29, 2022. doi:10.1016/j.amjsurg.2022.03.046