Psammoma body

A group of concentric, intracellular calcium collections seen in certain neoplasms such as Thyroid cancer#Papillary thyroid carcinoma, papillary serous endometrial cancer, mesothelioma, meningioma, and serous papillary cystadenocarcinoma of ovarian cancer. Can also appear in chronically inflamed tissue.
The formation of psammoma bodies is generally understood as a form of dystrophic calcification, a process where calcium salts are deposited in degenerating or necrotic (dead) tissue. Tumor cells, especially at the tips of finger-like "papillary" structures common in these cancers, can die due to lack of blood supply. These dead cells become a core (nidus) for calcium to layer upon.