Review of the touch preparation cytology of spindle epithelial tumor with thymus-like differentiation

Abstract

We experienced a case of spindle epithelial tumor with thymus-like differentiation (SETTLE) with touch preparation cytology performed during the intraoperative frozen section diagnosis in a 22-year-old woman. The tumor was partially encapsulated by fibrous capsule. It was a highly cellular biphasic tumor characterized by fasciculated spindle cells with streaming pattern and tubulopapillary epithelial component. The tumor cells were positive for cytokeratin, vimentin, c-kit, epithelial membrane antigen (EMA), and thyroid transcription factor-1 (TTF-1). However, the tumor cells were negative for thyroglobulin, calcitonin, CD99, S-100 protein, CD34, smooth muscle actin, HBME-1, and galectin-3. The reviewed touch smears showed tight clusters with high cellularity. Most cellular clusters showed papillary configuration. However, some clusters showed spindle cells with streaming pattern. The spindle tumor cells showed elongated and cigar-shaped nuclei. Although the incidence is very rare, SETLLE should be included in the differential diagnosis when a spindle cell neoplasm is encountered in touch preparation cytology in young patients with a thyroid mass.

Spindle epithelial tumor with thymus-like differentiation: A case report and literature review*

“…The tumor is commonly bifurcated and characterized by spindle-shaped epithelial cells mixed with thymus-like structures. However, rarely, it can be unidirectional and consist of spindle cells or thymus-like structures [9] reviewed eight cases in the literature that were diagnosed using fine needle aspiration cytology. These cases were described only morphologically with respect to cytological diagnosis.…”