Survival impact of psammoma body, stromal calcification, and bone formation in papillary thyroid carcinoma

The presence of calcification is the most significant ultrasonographic finding in evaluating thyroid nodules. Calcifications are more frequently detected in papillary thyroid carcinoma than in other thyroid lesions. However, the clinical significance of calcification, including clinical correlations and impact on survival, and the molecular mechanism responsible for calcification in papillary thyroid carcinoma remain uncertain. We performed a retrospective study of patients with primary common-type papillary thyroid carcinoma to determine the clinical correlations of calcification and its impact on survival. Histologically, calcification was classified as either psammoma bodies, stromal calcification, or bone formation. They were identified in 25, 47, and 13% of all 229 cases of papillary thyroid carcinoma, respectively. The presence of psammoma bodies was significantly correlated with gross lymph node metastasis and stage grouping. Both stromal calcification and bone formation were significantly correlated with patient age. In addition, stromal calcification was associated with pT classification and gross lymph node metastasis. Papillary thyroid carcinoma with, compared to that without, psammoma bodies was associated with poorer disease-free survival. We examined the quantitative expression of BMP-1, a metalloproteinase that is reported to be involved in bone and extracellular matrix formations, and found that its expression was significantly higher in tumors with psammoma bodies or with stromal calcification (P=0.0464 and 0.0272, respectively). These results suggest that the presence of psammoma bodies is a useful predictor of outcome for patients suffering from papillary thyroid carcinoma.