Outcome of Radical Resection and Postoperative Radiotherapy for Thyroid Carcinoma Showing Thymus‐like Differentiation

Abstract

Carcinoma showing thymus-like differentiation (CASTLE) is a rare disease that is difficult to diagnose. The aim of this study was to assess the effects of combined-modality treatment in CASTLE patients. We retrospectively studied patients identified between January 1, 2000 and December 31, 2009 as having CASTLE and who subsequently underwent surgery and radiotherapy or chemotherapy. Preoperative laboratory findings, ultrasonographic (US) and computed tomographic (CT) features, and fine-needle aspiration biopsy (FNAB) specimens were evaluated. Seven patients with CASTLE were identified (four men, three women). The median age at initial diagnosis was 48 years (range 25-56 years). The five newly diagnosed patients were treated with curative surgery and postoperative radiotherapy, whereas two patients with recurrent disease were treated with salvage surgery plus radiotherapy or chemotherapy. All patients were disease-free at a median follow-up period of 34 months (range 12-61 months). The pattern of immunohistochemical staining was similar to that of thymic carcinoma. Specimens from all seven patients stained positively for CD5, CD117, and cytokeratin but were uniformly negative for thyroglobulin, thyroid transcription factor 1 (TTF-1), and calcitonin. Patients with CASTLE have excellent outcomes after curative resection and postoperative radiotherapy compared with patients with anaplastic thyroid carcinoma. Even patients with local recurrent disease benefited from salvage surgery with subsequent operation and/or radiotherapy. CD5 immunohistochemical staining on FNAB samples may help identify the possible entities that are part of the differential diagnosis.