# Hide-and-Seek With Spindle-Cell-Component-Poor Metaplastic Thymoma

## TL;DR

This paper describes a rare case of metaplastic thymoma that resembles a more common type A thymoma and is linked to psoriasis.

## Contribution

The first published case of metaplastic thymoma with associated psoriasis and sparse spindle-cell component.

## Key findings

- Metaplastic thymoma with minimal spindle-cell component can mimic type A thymoma histologically.
- Immunohistochemical analysis helps distinguish metaplastic thymoma from type A thymoma.
- This case is the first to report metaplastic thymoma co-occurring with psoriasis.

## Abstract

Metaplastic thymoma is a rare biphasic thymic tumor with indolent behavior and recurrent YAP1::MAML2 gene rearrangement. Although the diagnosis of this tumor is usually straightforward based on hematoxylin and eosin (H&E) findings alone, cases with scant spindle-cell (“pseudosarcomatous stroma“) components can be easily confused with more commonly occurring type A thymoma. We present a case of metaplastic thymoma with a sparse stroma-like spindle-cell component, discussing its histological and immunohistochemical hints and drawing attention to the visual similarity to type A thymoma. This is also the first published case of metaplastic thymoma with associated psoriasis.