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Abstract

OBJECTIVE:

Metastatic lymph node ratio (MLNR) is a known significant predictor of disease-free survival in differentiated thyroid cancer. The authors investigated the ability of preoperative fluorine-18 fluorodeoxyglucose (F-FDG) PET/CT to predict recurrence after surgery with radioactive iodine therapy considering MLNR.

PATIENTS AND METHODS:

A total of 274 patients who underwent preoperative PET/CT and surgery with radioactive iodine therapy were enrolled. The tumor-to-liver uptake ratio on PET/CT was calculated by dividing the maximum standardized uptake value of a primary lesion by the mean standardized uptake value of the normal liver. High F-FDG uptake was defined as tumor-to-liver uptake ratio more than the median cutoff value (2.1). MLNR was calculated by dividing the number of metastatic lymph nodes (LNs) by the number of cervical LNs removed. A high MLNR was also defined as one more than a threshold value (0.4), identified by plotting Kaplan-Meier survival curves and comparing them using the log-rank test. The prognostic significances of clinicopathologic variables were analyzed.

RESULTS:

Fifteen (5.5%) patients developed recurrence in the thyroid bed or in cervical LNs. Cox regression analysis showed that a high MLNR was significantly associated with a worse disease-free survival (odds ratio 6.95; 95% confidence interval: 2.36-20.47; P<0.001). A subgroup analysis of 70 patients with a high MLNR showed that only high F-FDG uptake was significantly associated with a worse disease-free survival (odds ratio 5.77; 95% confidence interval: 1.22-27.16; P=0.027).

CONCLUSION:

High F-FDG uptake of primary lesion on preoperative PET/CT has selective prognostic value according to the extent of metastatic LNs (MLNR>0.4).​ 

Author information

Kwon SY1, Choi EK, Kong EJ, Chong A, Ha JM, Chun KA, Cho IH, Bom HS, Min JJ, Kim J, Song HC, O JH, Kim SH.

1 aDepartment of Nuclear Medicine, Chonnam National University Hwasun Hospital bDepartment of Radiology, Incheon St. Mary's Hospital, College of Medicine, The Catholic University of Korea cDepartment of Nuclear Medicine, Yeungnam University Medical School and Hospital dDepartment of Nuclear Medicine, Chosun University Hospital eDepartment of Nuclear Medicine, Chonnam National University Hospital fDepartment of Radiology, Seoul St. Mary's Hospital, College of Medicine, The Catholic University of Korea.