In differential diagnosis, thymic diseases, thyroid goiter, NUT carcinoma (a rare SALL4- and AFP-expressing poorly differentiated squamous cell cancer), metastatic melanoma, sarcomas (the SMARCA4-deficient subtype often expresses SOX2, SALL4, and vimentin), lymphomas (which can be identified with CD45a and B/T cell markers), and metastatic carcinoma to the mediastinum should be considered. The gene discussed is SALL4; the disease is nut midline carcinoma.