Diagnostic pitfalls of fine-needle aspiration cytology and prognostic impact of chemotherapy in thyroid lymphoma.

BACKGROUND AND PURPOSE Fine-needle aspiration cytology (FNAC) is an important method in the evaluation of goiter. However, difficulties are encountered when using this technique to distinguish Hashimoto's thyroiditis from thyroid lymphoma. This study sought to determine the diagnostic sensitivity of FNAC and to determine the effectiveness of chemotherapy in the treatment of thyroid lymphoma. METHODS We retrospectively reviewed the clinical manifestations, diagnostic methods, treatment, and prognosis in 14 consecutive patients with histopathology-verified thyroid lymphoma treated in National Taiwan University Hospital from 1981 to 2000. RESULTS Eleven of the 14 patients underwent FNAC, which identified six lymphomas, one anaplastic carcinoma, three cases of Hashimoto's thyroiditis, and one case of Riedel's struma. Because all cases were promptly biopsied, the mean survival times for patients with or without the correct initial diagnosis (15 mo vs 43 mo) did not differ significantly (p = 0.098 by Student's t-test). Thyroid lymphoma was diagnosed before 1990 in four patients, three of whom were treated with local radiotherapy and one with surgical resection. The mean survival time of these four patients was 60 days. Thyroid lymphoma was diagnosed after 1990 in 10 patients, nine of whom underwent systemic chemotherapy, with additional adjunctive radiotherapy in three patients. The mean survival time in the nine of these 10 patients with follow-up was 60 months. A significant difference was found in the mean disease-free survival times between patients treated before and after 1990 (60 d vs 60 mo, p = 0.005). CONCLUSIONS In this study, FNAC had a sensitivity of only 55%, its major limitation being misdiagnosis of lymphoma as Hashimoto's thyroiditis in three patients. However, such initial misdiagnosis does not affect the prognosis if promptly corrected by histopathology. As evidenced by the improved survival of patients receiving chemotherapy after 1990, we conclude that chemotherapy is effective in the treatment of thyroid lymphoma.