Evaluation of CYFRA 21.1 as a Dedifferentiation Marker of Advanced Thyroid Cancer

PURPOSE OF THE STUDY: Well-differentiated thyroid carcinomas have good prognosis, but as it de-differentiates, the survival rates go down. Early identification of such patients needs a marker which indicates the dedifferentiation process. CYFRA 21.1 has also shown to be increased in patients with (131)I refractory thyroid cancer. We tested whether CYFRA 21.1 can differentiate between (131)I avid and refractory tumors. METHODOLOGY: Well-differentiated thyroid cancer patients with known distant metastases were accrued and tested for stimulated and unstimulated thyroglobulin and CYFRA 21.1. All patients underwent (131)I whole-body scan, (131)I post therapy scan, and (18)F-Fluorodeoxyglucose positron emission tomography-computed tomography. Those with even a single (131)I nonavid lesion were considered (131)I refractory disease. CYFRA 21.1 of both (131)I avid and nonavid was compared, and CYFRA 21.1 levels against disease extent were analyzed. RESULTS: CYFRA 21.1 levels were significantly elevated in (131)I refractory group. A cutoff value of 2.07 ng/ml distinguished between (131)I avid and refractory disease with high sensitivity and specificity (88% and 89. 7%, respectively). However, CYFRA 21.1 levels were similar in patients when analyzed based on disease sites. CONCLUSION: CYFRA 21.1 can be utilized to differentiate between (131)I avid and refractory diseases. Further long-term studies are required to use it as a predictive and prognostic marker.