Classification of Thyroid Tumors

The conventional classification based on morphology and clinical features is largely supported by molecular data currently available. Genetic profiles of four main categories appear distinctly different from each other with a few areas of overlap.

The classification of thyroid tumors modified from WHO classification (2004) is as follows:

Tumors of Follicular Epithelium:
■„Follicular adenoma (including Hurthle cell adenoma)
■„Hyalinizing trabecular adenoma ■„Follicular carcinoma (including Hurthle cell carcinoma)
– Minimally invasive – – Widely invasive
■„Papillary carcinomas
■„Poorly differentiated carcinoma ■„Anaplastic carcinoma
■„Squamous cell carcinoma ■„Mucoepidermoid carcinoma ■„Sclerosing mucoepidermoid carcinoma with eosinophilia ■„Mucinous carcinoma

Tumors with C Cell Differentiation
Medullary carcinoma

Tumors with Mixed Differentiation
■„Collision tumor—follicular/papillary or follicular/medullary
■„Mixed differentiated carcinoma intermediate type

Tumors Showing Thymic or Related Branchial Pouch Differentiation
■„Ectopic thymoma
■„Spindle epithelial tumor with thymus-like
element (SETTLE)
■„Carcinoma showing thymus-like element (CASTLE).

Tumors of Lymphoid Cells
■„Malignant lymphoma ■„Plasmacytoma

Mesenchymal Tumors
■„Smooth muscle tumors ■„Peripheral nerve sheath tumors ■„Paragangliomas
■„Solitary fibrous tumors ■„Follicular dendritic cell tumors ■„LCH



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