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 with¹³¹I refractory thyroid cancer. We tested whether CYFRA 21.1 can differentiate between¹³¹I 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 underwent¹³¹I whole-body scan,¹³¹I post therapy scan, and¹⁸F-Fluorodeoxyglucose positron emission tomography-computed tomography. Those with even a single¹³¹I nonavid lesion were considered¹³¹I refractory disease. CYFRA 21.1 of both¹³¹I avid and nonavid was compared, and CYFRA 21.1 levels against disease extent were analyzed. Results: CYFRA 21.1 levels were significantly elevated in¹³¹I refractory group. A cutoff value of 2.07 ng/ml distinguished between¹³¹I 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 between¹³¹I avid and refractory diseases. Further long-term studies are required to use it as a predictive and prognostic marker.