917 Metaplastic Thymic Sarcoma of The Thyroid: A Case Report and A Review of The Literature

Abstract

Abstract In this paper, the authors present a case diagnosed as ‘metaplastic thymic sarcoma’. Tumours of the thymus are extremely rare: there is a disparity in terminology and histology observed, although there have been efforts to make classification clearer. The reported case concerns a seventy-eight-year-old woman, who presented with a rapidly enlarging neck mass. Histological diagnosis was made challenging by the unusual characteristics of the tumour; the diagnosis of ‘metaplastic thymic sarcoma’ was eventually established, following consultation with an internationally renowned soft tissue pathologist. Review of the relevant literature demonstrated no comparable cases; the presentation of a thymic tumour within the thyroid is also considered unusual. The tumour observed did not conform to any previously sub type of thymic tumour and is therefore believed to be a distinct entity. The patient suffered aggressive recurrence of the disease shortly after her surgery. Genetic testing indicated the tumour was BRAF positive, and there was a dramatic clinical response to Dabrafenib/ Trametinib treatment. The successful use of immunotherapy is encouraging finding, however the diagnosis of another distinct sub type of thymic tumour, further demonstrates the diagnostic and therapeutic challenges presented by this rare and heterogenous group.