Histopathological and immunohistochemical features of thyroid carcinoma

Thyroid-specific malignant tumors are derived from follicle cells (papillary and follicular carcinoma), and from parafollicular, calcitonin-producing C-cells (medullary carcinoma). The main criterion for diagnosis of papillary carcinoma is the occurrence of ground glass, hypochromic nuclei, often associated with papillae as the prominent pattern of the tumor, and psammoma bodies. The diagnosis of follicular carcinoma is based on the true infiltration of the venous vessels outside the tumor capsule and the fungus-like infiltration through the tumor capsule into the surrounding parenchyma. Anaplastic carcinoma is mostly detected by the pathologist by fine-needle aspiration biopsy, or tumor reduction specimen. Medullary thyroid carcinoma is typically composed of solid nests and infiltrating formations of polygonal or spindle-shaped cells and amyloid deposits within the stroma of the tumor. Two main discriminatory immunohistochemical markers for tumors with follicular and parafollicular origin are thyroglobulin and calcitonin, respectively. Thyroglobulin is present in more than 95% of papillary and follicular carcinomas, whereas anaplastic thyroid carcinomas are mostly immunonegative for thyroglobulin. Medullary carcinoma is characteristically positive for calcitonin, pan-neuroendocrine markers, and often numerous peptides