Growth Kinetics of Macronodular Lung Metastases and Survival in Differentiated Thyroid Carcinoma

Background: The clinical course of patients with lung metastases of differentiated thyroid carcinoma (DTC) vary, and cancer-specific survival (CSS) can be associated with tumor burden. This study evaluated the growth kinetics of lung metastases from DTC using serial chest computed tomography for Response Evaluation Criteria in Solid Tumors assessment and its prognostic implications. Methods: Forty-four patients with macronodular lung metastases (≥1 cm) of DTC were included. The time intervals to disease progression of lung metastases were measured and compared to CSS rates. Results: On the basis of the time to progression, 15 (34%), 17 (39%), and 12 (27%) patients were classified into the slow (≥3 years), moderate (1-3 years), and rapid groups (<1 year), respectively. The growth kinetics of lung metastases exhibited a linear pattern in the three groups. The doubling time of tumor burden was 1.8 years (R² = 0.973, p = 0.013) in the rapid group, and the estimated doubling time of the tumor burden in the moderate and slow groups was 5.9 years and 19.3 years, respectively. No independent variable predicted the growth kinetics of lung metastases. In multivariate analysis, disease progression within the first year was an independent predictor of CSS (hazard ratio = 8.6; p = 0.003). Conclusions: This is the first study to demonstrate objectively that tumor growth kinetics within the first year are an independent predictor of CSS in patients with macronodular lung metastases. Performing chest computed tomography at least twice a year in the early phase of the disease in patients with macronodular lung metastases may be helpful for identifying high-risk patients who are eligible for treatment with tyrosine kinase inhibitors.