Papillary thyroid carcinoma: evidence for intracytoplasmic formation of precursor substance for calcification and its release from well-preserved neoplastic cells.

Psammoma bodies (PBs) are believed to represent a process of dystrophic calcification over nonviable and dying tissues. Light microscopic and ultrastructural observations suggest that PB formation follows the intracellular assembly of precursor substances and their calcification leading to death of tumor cells and their release. It may also be the result of local secretion of precursor substances like collagen by tumor cells into extracellular space and their calcification. In an earlier reported study, we demonstrated the extracellular localization of various precursor forms of PBs and of irregular calcification in fine-needle aspiration (FNA) smears of papillary thyroid carcinoma (PTC). In this report, we describe a PTC case with intracellular formation precursor substances for calcification and their release from the well-preserved neoplastic cells before undergoing calcification. Ultrasound-guided FNA smears from a small nodule in the left lobe of thyroid in a 40-year-old woman revealed a PTC with numerous intracytoplasmic targetoid bodies, which were magenta colored in MGG stain. On their release from the neoplastic cells, these targetoid precursor bodies were found to be forming pools of matrix material, some of which showed evidence of calcification. The cytologic findings were confirmed by histopathology of the tumor in the thyroidectomy specimen. For the first time, we demonstrate through cytomorpholgy the intracytoplasmic formation of targetoid bodies as precursor substances for calcification and their release from well-preserved cells in PTC. We suggest that the calcification in PTC may not necessarily be taking place over nonviable and dying cells.