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

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.

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.

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.

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.