Anaplastic thyroid carcinoma: an epidemiologic, histologic, immunohistochemical, and molecular single-institution study.

Anaplastic thyroid carcinoma (ATC) is a highly aggressive form of thyroid cancer. A single-institution thyroid cancer cohort of ATC was identified within the last 10 years at our institution. Retrospective analysis revealed that the frequency of ATC was 0.5% (11/2106 thyroid carcinomas). The average age at diagnosis of ATC was 74 years, and the female-to-male ratio was 1.2:1. ATC presented as a rapidly enlarging neck mass involving predominantly the left thyroid lobe (7/11; 64%). Cervical adenopathy was present in 7 (64%) of 11 cases. Fifty-five percent (6/11) of patients had distant metastases at the time of diagnosis. Histologically, ATC closely simulated a large variety of soft tissue sarcomas; osteoclast-like giant cell-rich tumors; squamous cell, spindle cell, and small cell carcinomas; and anaplastic/large cell lymphomas. Four tumors (4/11; 36%) showed heterologous elements, including rhabdoid and chondroid differentiation. Immunohistochemical studies showed that all ATCs lost TTF-1 and thyroglobulin expression, whereas PAX-8 expression was identified in 36% (4/11) of tumors. Intense and extensive nuclear staining of p53 (>50%) and high Ki-67 proliferative rate (>30%) were seen in all ATCs (11/11; 100%). Next-generation sequencing revealed recurrent BRAF V600E and TP53 gene mutations. Individual examples of a BRAF G469A mutation in ATC with follicular carcinoma component, EGFR, PTEN, PIK3CA, and FGFR3 mutations, were also identified, whereas 1 case of ATC showed wild-type sequencing with no identifiable alterations.