Long-term outcome of rare oncocytic papillary (Hürthle cell) thyroid carcinoma following (adjuvant) initial radioiodine therapy.

PURPOSE: Oncocytic (Hürthle cell) papillary thyroid carcinoma (OPTC) is a rare variant of the papillary thyroid carcinoma (PTC) which comprises approximately 1 to 11 % of PTC cases. Its clinical course and prognosis have not been comprehensively documented and the clinical outcome remains a controversial issue. Therefore, we investigated the long-term prognosis after thyroidectomy and (adjuvant) initial radioactive iodine therapy (RIT) of OPTC compared to PTC. METHODS: A total of 563 patients (47 with OPTC and 516 with PTC) with a median follow-up of 9.9 (0.3; 23.5) years were studied. All patients underwent thyroidectomy followed by (adjuvant) initial RIT. Data on the patients' demographics, pathology, laboratory findings, imaging studies, treatment, and follow-up including recurrence, and disease-specific survival were collected. Cox's multivariate regression model was used to identify independent prognostic factors for survival. RESULTS: OPTC patients were significantly older (55.2 ± 12.3 years) than PTC patients (50.3 ± 13.5) at the time of initial diagnosis (p value 0.016). Initial tumor size was larger in the OPTC group (2.8 ± 1.8 cm for OPTC patients, 1.5 ± 1.2 cm for PTC patients, p value < 0.001). Before matching, OPTC patients presented more often with evidence of disease at the last visit of follow-up (p value 0.046). However, this difference was not observed anymore after matching for risk factors (p value 0.637). Disease-specific survival did not differ significantly. Age (HR, 1.183; 95% CI, 1.097-1.276) was identified as an independent prognostic factor for disease-specific survival. OPTC patients predominantly showed a recurrence of distant metastasis within a shorter time despite being not statistically significant. CONCLUSION: At initial diagnosis, OPTC shows significant differences in terms of age and initial tumor size compared to PTC. Patients suffering from OPTC present with the same clinical long-term outcome indifferent to PTC after (adjuvant) initial RIT after matching.

Suspected recurrence of brain metastases after focused high dose radiotherapy: can [18F]FET- PET overcome diagnostic uncertainties?

BACKGROUND: After focused high dose radiotherapy of brain metastases, differentiation between tumor recurrence and radiation-induced lesions by conventional MRI is challenging. This study investigates the usefulness of dynamic O-(2-18F-Fluoroethyl)-L-Tyrosine positron emission tomography (18F-FET PET) in patients with MRI-based suspicion of tumor recurrence after focused high dose radiotherapy of brain metastases. METHODS: Twenty-two patients with 34 brain metastases (median age 61.9 years) were included. Due to follow-up scan evaluations after repeated treatment in a subset of patients, a total of 50 lesions with MRI-based suspicion of tumor recurrence after focused high dose radiotherapy could be evaluated. 18F-FET PET analysis included the assessment of maximum and mean tumor-to-background ratio (TBRmax and TBRmean) and analysis of time-activity-curves (TAC; increasing vs. decreasing) including minimal time-to-peak (TTPmin). PET parameters were correlated with histological findings and radiological-clinical follow-up evaluation. RESULTS: Tumor recurrence was found in 21/50 cases (15/21 verified by histology, 6/21 by radiological-clinical follow-up) and radiation-induced changes in 29/50 cases (5/29 verified by histology, 24/29 by radiological-clinical follow-up). Median clinical-radiological follow-up was 28.3 months (range 4.2-99.1 months). 18F-FET uptake was higher in tumor recurrence compared to radiation-induced changes (TBRmax 2.9 vs. 2.0, p < 0.001; TBRmean 2.2 vs. 1.7, p < 0.001). Receiver-operating-characteristic (ROC) curve analysis revealed optimal cut-off values of 2.15 for TBRmax and 1.95 for TBRmean (sensitivity 86 %, specificity 79 %). Increasing TACs and long TTPmin were associated with radiation-induced changes, decreasing TACs with tumor recurrence (p = 0.01). By combination of TBR and TACs, sensitivity and specificity could be increased to 93 and 84 %. CONCLUSIONS: In patients with MRI-suspected tumor recurrence after focused high dose radiotherapy, 18F-FET PET has a high sensitivity and specificity for the differentiation of vital tumor tissue and radiation-induced lesions.