A late-relapse germ cell tumor might contain malignant non-germ cell tumors, known as 'somatic-type malignancy (SM)'. The development of a secondary SM is rare, and this phenomenon remains poorly understood. Case 1 developed lung metastasis 13 years after chemotherapy followed by retroperitoneal lymph node dissection for stage IIA non-seminoma. The tumor increased in size after chemotherapy. The patient underwent a pneumonectomy. Pathology revealed an adenocarcinoma with immature teratoma. The patient has experienced no relapse for 9 years. Case 2 developed a pelvic tumor after 10 years of surveillance for stage I seminoma. The tumor increased in size after chemotherapy. The patient underwent pelvic tumor resection with cystectomy. Pathology revealed a mature teratoma with SMs consisting of sarcoma and adenocarcinoma. The patient has experienced no relapse for 6 months. Surgical resection played a major role in the treatment of very late-relapse germ cell tumors with SM.