After excluding the possibility of a metastatic tumor, differential diagnosis of the primary tumor included several possible types of tumors: chordoma, extraskeletal myxoid chondrosarcoma, myoepithelioma/mixed tumor, benign peripheral nerve sheath tumor showing myxoid change, chondrosarcoma, myxoid liposarcoma, primary pulmonary myxoid sarcoma with EWSR1–CREB1 fusion, pleomorphic adenoma, chordoid meningioma, and mucinous carcinoma. The gene discussed is CREB1; the disease is mucinous adenocarcinoma.