Determining Whether Tumor Volume Doubling Time and Growth Rate Can Predict Malignancy After Delayed Diagnostic Surgery of Follicular Neoplasm.

Abstract

Background: Tumor volume doubling time (TVDT) is considered as a dynamic indicator of tumor growth and progression. We aimed to clarify whether TVDT should be considered in the cytological diagnosis of follicular neoplasms (FNs). Methods: This retrospective cohort study included 100 consecutive FN patients with a TVDT >1 year for whom surgical resection was delayed for >1 year. Changes in tumor volume and the TVDT of each nodule were calculated by serial neck ultrasonography (US) over a median follow-up of 50 months. Results: Among 100 surgically resected FNs, 58 (58%) were benign and 42 (42%) were malignant tumors. At the 5-year follow-up, most FN nodules showed volume increases of >50%, accounting for 65% of benign and 62% of malignant nodules. No significant difference was observed in tumor growth rates and time to a >50% increase in tumor volume between benign and malignant nodules (p = 0.299 and p = 0.378, respectively). The calculated TVDT and a >50% volumetric increase showed a linear relationship with a high concordance (R2 = 0.883; p < 0.001). The risk of malignancy was not significantly associated with TVDT (relative risk = 1.00; [95% confidence interval 0.99-1.01]; p = 0.784). Even when US features were considered, no significant association was found between TVDT and the risk of malignancy. Conclusions: The size of most FNs increased exponentially with time; the tumor growth rates of benign and malignant nodules were similar. Despite the usefulness of TVDT as an indicator of growing velocity of FN nodules, TVDT could not predict malignancy in FNs. Clinical surveillance based on the growth of thyroid nodules categorized as FNs on serial neck US does not predict the risk of malignancy.