Pleomorphic undifferentiated sarcoma of the mediastinal thymus: A case report and literature review.

Pleomorphic undifferentiated sarcoma (PUS) of the mediastinal thymus is a rare type of cancer. In the present case report, a 67-year-old female patient presenting a mediastinal mass for >1 year was assessed for clinical characteristics, histopathological, immunohistochemical expression and gene mutation using fluorescence hybridization (FISH), and relevant literature was reviewed. Histological analysis revealed nodular changes of different sizes in the thymus, which consisted of a mixture of pleomorphic and spindle cells. The pleomorphic cells with distinct atypia were giant cells and multinucleated cells with large cell sizes and frequent nuclear divisions. The spindle cells were mild to moderate atypical and arranged in a woven pattern, and nuclear division was rare. Immunohistochemical analysis indicated that vimentin was diffusively expressed in tumor cells. No amplification was found in CDX2 and MDM4 genes using the FISH analysis. In conclusion, mediastinal thymus neoplasm should be considered in the presence of PUS and it is an exclusionary diagnosis based on clinical and pathological examination of the patient.