Background: Estimating the growth rate of lung metastases in patients with metastases of differentiated thyroid carcinoma (DTC) is important as their clinical courses are associated with the progression of the lung metastases. This study aimed to evaluate survival outcomes using different criteria for estimating the tumor growth rate.
Methods: Patients with ≥1cm lung metastases of DTC who underwent total thyroidectomy and high-dose radioactive iodine therapy were enrolled. The time to progressive disease (PD) by Response Evaluation Criteria in Solid Tumors (RECIST), tumor volume doubling time (TVDT) of the two dominant target lung lesions, and thyroglobulin doubling time (TgDT) were measured in each patient, and their association with disease-specific survival (DSS) was evaluated.
Results: Forty-four patients with target lung metastatic nodules with an initial maximal diameter of 1.3 cm (median) were followed up for a median of 6.8 years after the diagnosis of lung metastases. Based on RECIST, 12 patients (27.3%) showed fast tumor progression, with time to PD <1 year. When assessed by TVDT, 9 patients (20.5%) had TVDT ≤1 year, showing rapid tumor progression. Seven of 33 patients (21.2%) who were negative for thyroglobulin antibody had TgDT <1 year. Growth rates assessed by all three criteria were significantly associated with DSS. However, TVDT had the highest predictive value for DSS, with a proportion of variation explained of 34.3%. Five-year DSS was 29.6% in patients with TVDT ≤1 year, 50.0% in patients with time to PD <1 year, and 42.9% in patients with TgDT <1 year.
Conclusions: TVDT was the most powerful for predicting DSS, in comparison with RECIST and TgDT. Performing at least three serial chest computed tomography scans during the first year from the diagnosis of lung metastases can assist in early detection of patients with rapid tumor progression and provide objective guidance for initiation of systemic therapy.