Spindle Cell Metaplasia of the Thyroid
Spindle Cell Metaplasia of the Thyroid
Spindle cell proliferations of the thyroid have been described in association with reactive processes and aggressive malignant neoplasms. We describe spindle cell proliferations in 10 patients arising in association with papillary carcinoma and follicular adenoma. The spindle proliferations were 0.3 to 3.0 cm in size, constituted from 1% to 95% of the primary neoplasm, and were either admixed with the neoplastic elements or peripherally located within the primary tumor. Cytologically, these proliferations showed bland-appearing spindle cells with fine chromatin and subtle nucleoli. Mitoses were rare, and inflammation was minimal. Immunostains showed reactivity with thyroglobulin, indicating their follicular origin. We believe it is important to recognize these metaplastic proliferations and distinguish them from aggressive malignant neoplasms.
Spindle cell lesions of the thyroid are rare. They can be of primary thyroid origin or arise secondary to metastatic disease. Lesions of primary thyroid origin can be derived from follicular, C-cell (parafollicular), or mesenchymal components. They can manifest either as reactive proliferations, as in the case of post—fine-needle aspiration spindle cell nodules of the thyroid, or as neoplastic processes such as anaplastic carcinoma, medullary carcinoma, solitary fibrous tumor, and sarcoma. Distinction among these processes is critical, as it dictates therapy and defines patient prognosis. Interpretation of specimens can be difficult and requires immunohistochemical staining to determine the cellular origin of these lesions. We describe 10 cases of spindle cell proliferations in the thyroid arising in association with papillary carcinoma and follicular adenoma, and we discuss the pathologic features and immunohistochemical reactivity patterns that suggest these may result from metaplastic transformation of follicular epithelium.
Spindle cell proliferations of the thyroid have been described in association with reactive processes and aggressive malignant neoplasms. We describe spindle cell proliferations in 10 patients arising in association with papillary carcinoma and follicular adenoma. The spindle proliferations were 0.3 to 3.0 cm in size, constituted from 1% to 95% of the primary neoplasm, and were either admixed with the neoplastic elements or peripherally located within the primary tumor. Cytologically, these proliferations showed bland-appearing spindle cells with fine chromatin and subtle nucleoli. Mitoses were rare, and inflammation was minimal. Immunostains showed reactivity with thyroglobulin, indicating their follicular origin. We believe it is important to recognize these metaplastic proliferations and distinguish them from aggressive malignant neoplasms.
Spindle cell lesions of the thyroid are rare. They can be of primary thyroid origin or arise secondary to metastatic disease. Lesions of primary thyroid origin can be derived from follicular, C-cell (parafollicular), or mesenchymal components. They can manifest either as reactive proliferations, as in the case of post—fine-needle aspiration spindle cell nodules of the thyroid, or as neoplastic processes such as anaplastic carcinoma, medullary carcinoma, solitary fibrous tumor, and sarcoma. Distinction among these processes is critical, as it dictates therapy and defines patient prognosis. Interpretation of specimens can be difficult and requires immunohistochemical staining to determine the cellular origin of these lesions. We describe 10 cases of spindle cell proliferations in the thyroid arising in association with papillary carcinoma and follicular adenoma, and we discuss the pathologic features and immunohistochemical reactivity patterns that suggest these may result from metaplastic transformation of follicular epithelium.
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