We herein report a 47-year-old man who presented with progressive paraparesis. Imaging revealed a right upper pulmonary nodule, massive bilateral adrenal metastases, thoracolumbar vertebral osteolysis, and subcutaneous nodules. A biopsy of the right buttock nodule revealed a poorly differentiated metastatic carcinoma with high programmed cell death-ligand 1 expression and extensive chromosomal rearrangements. The patient died 10 days after the initiation of pembrolizumab treatment. Autopsy findings confirmed pulmonary pleomorphic carcinoma with extensive metastases. Quantification of chromosomal rearrangements revealed a jump-up mutation from the normal karyotype, followed by a further incremental increase in the degree of deviation.