Natural History of Asymptomatic Papillary Thyroid Microcarcinoma: Time-Dependent Changes in Calcification and Vascularity During Active Surveillance

Background: Prospective trials of non-surgical observation have shown progression rates of only 5-10% in patients with asymptomatic papillary microcarcinoma (PMC). This study investigated time-dependent changes in calcification patterns and tumor vascularity on ultrasonography (US) to clarify the natural course of PMC.

Methods: We examined calcification patterns and tumor vascularity for 480 lesions in 384 patients. Calcification patterns were classified as: (A) none; (B) micro; (C) macro; or (D) rim. Tumor vascularity was classified as rich or poor via color Doppler US.

Results: After a mean of 6.8 years of observation, 29 lesions (6.0%) had increased in size. Mean age for initial calcification pattern was 52.1 years for A (n = 135), 54.2 years for B (n = 235), 56.3 years for C (n = 96), and 60.1 years for D (n = 14), and the incidence rates of tumor enlargement were 9.6, 5.5, 3.2, and 0%, respectively. The cumulative rate of upgrade in calcification pattern was 51.8% at 10 years. Lesions with initially rich vascularity (n = 70) had significantly higher rate of tumor enlargement than those with poor vascularity (n = 410); however, the majority of tumor (61.4%) with initially rich vascularity had decreased their blood supply during the follow-up. Multivariate analysis showed that strong calcification (C or D) and poor vascularity at last examination correlated significantly with non-progressive disease.

Conclusions: PMCs in older patients showed significantly stronger calcification patterns and poorer vascularity. Both consolidation of calcification and loss of vascularity occurred in a time-dependent manner during observation and were significant indicators for non-progressive disease.