Fine-needle aspiration biopsy of secondary neoplasms of the thyroid gland: A multi-institutional study of 62 cases

BACKGROUND Secondary neoplasms of the thyroid gland (SNTGs) are uncommon, and it is important to recognize them in thyroid fine-needle aspiration biopsy (FNAB). METHODS The authors report a cohort of 62 SNTGs from 7 institutions in the United States and Europe. Patients were identified retrospectively by searching through medical records of the respective institutions. All initial diagnoses were rendered by FNAB. RESULTS SNTGs represented 0.16% of all thyroid FNABs and were more frequent among women (ratio of women to men, 1.2:1.0). The mean patient age was of 59 years (range, 7-84 years), the mean tumor size was 3 cm (range, 0.9-7 cm), and the mean interval from diagnosis of the primary tumor was 45 months (range, 0-156 months). Eighty-seven percent of SNTGs were diagnosed as malignant by FNAB, and there was a specific SNTG diagnosis in 93% of patients. Immunocytochemistry and flow cytometry, which were used in 30% of patients, were useful ancillary studies. Adenocarcinomas (n = 23; 37%) and squamous cell carcinomas (SCCs) (n = 22; 35.5%) represented the majority of SNTGs, followed by lymphoma (n = 5; 8%), melanoma (n = 5; 8%), adenoid cystic carcinoma (n = 3; 5%), and various sarcomas (n = 3; 5%). Adenocarcinomas originated from the kidney (n = 9; 39%), lung (n = 6; 26%), breast (n = 5; 22%), and colon (n = 3; 13%). SCCs originated mostly from the head and neck (n = 13; 59%), followed by lung (n = 3; 13%), esophagus (n = 3; 14%), and unknown primary sites (n = 3; 14%). CONCLUSIONS Adenocarcinomas from the kidney, lung, breast, and colon along with SCCs represent the majority of SNTGs. The current results indicate that FNAB is a sensitive and accurate method for diagnosing SNTG; however, diagnostic difficulties can occur. Knowledge of clinical history and the judicious application of ancillary studies can increase the sensitivity and accuracy of FNAB for detecting SNTGs.