Cooccurrence of myelodysplastic neoplasm and myeloid sarcoma with background mediastinal germ cell tumor: an autopsy case

Hematological malignancy (HM) is developed in 2–6% patients with primary mediastinal germ cell tumor (MGCT). Symptoms of HM associated with MGCT usually appear after diagnosis of MGCT. Patients with MGCT underlying HM have poor prognosis. We report an extremely rare autopsy case of simultaneous presentation of MGCT, myelodysplastic neoplasm (MDS) with low blasts, and myeloid sarcoma (MS). A 27-year-old man presented with intermittent fever, general fatigue, and cough. Computed tomography revealed 11 cm mass in anterior mediastinum, hepatosplenomegaly, and gastric, pericholedochal, and mesenteric lymphadenopathies. The mass compressed the left pulmonary artery. Laboratory examination revealed thrombocytopenia (59,000 /mm3). Serological tests revealed elevated alpha-fetoprotein 7,219 ng/mL and human chorionic gonadotropin 899 IU/L. Bone marrow aspiration smear showed presence of micromegakaryocytes and blast count of 1.2%. G-banding detected monosomy 13 and complex karyotype. The autopsy revealed that MGCT was mainly composed of teratoma and also included yolk sac tumor, seminoma, and choriocarcinoma components. Transformation to acute myeloid leukemia was not observed in the bone marrow but CD33 and MPO-positive immature myeloid blasts proliferated in the lymph nodes, liver, spleen, and small intestine. Loss of p53 expression was observed in bone marrow and extramedullary immature myeloid blasts. Next gene sequencing detected TP53 c.919+3del splice site variant and KRAS N116H. It is important to consider HMs when extramediastinal lesions or thrombocytopenia appear in patients with MGCT.