Primary squamous cell carcinoma of the thyroid: report of ten cases

To define the clinical and pathologic characteristics of primary squamous cell carcinoma of the thyroid (PSCCT), a rare tumor, and compare it to the more common secondary squamous cell carcinoma of the thyroid (SSCCT).

A search of tumor registry and medical archives of our institution identified 24 cases of squamous cell carcinoma involving the thyroid in a 25-year period (1978-2003). Medical records and pathology specimens were reviewed. This investigation did not reveal other primary sites in 10 (PSCCT). Other primary sites were identified in 14 patients (SSCCT). Immunostaining was done for thyroglobulin, cytokeratin (7 and 19), thyroid transcription factor (TTF), calcitonin, p21, MIB-I, and p53.

All 10 PSCCTs presented with a rapidly enlarging neck mass. Excision was possible in 8. PSCCT had the following features on immunostaining: keratin (8/8, 100%), thyroglobulin (5/8, 62.5%), TTF positive (3/8, 37.5%), and calcitonin negative. Cytokeratins 7 and 19 were diffusely and strongly positive in the PSCCT. Expression of putative biomarkers p21, MIB-I, and p53 was elevated with PSCCT cells showing mean expression of 36%, 48%, and 39%, respectively, compared to less than 5% in non-neoplastic tissues. The mean survival from diagnosis was 8.6 months. All patients died of disease. Airway compromise was the cause of death in the majority. In SSCCT, positivity for thyroglobulin and TTF was not seen. The locations of the primary sites were: larynx (7; 50%), trachea (4; 29%), esophagus (2; 14%), and oral cavity (1; 7%). At last follow-up, 4 were alive with mean survival of 5.5 years. Six had cancer-related mortality with mean survival of 46 months.

PSCCT is an aggressive cancer with death occurring within the first year in most patients. The prognosis for patients with PSCCT is worse than SSCCT. p21, MIB-I, and p53 are overexpressed in PSCCT. Thyroglobulin and TTF can show focal positivity in PSCCT distinguishing it from SSCCT.