A 20-year-old Asian male patient, who had no family history of tumor and genetic diseases, presented with a painful anterior mediastinal mass in March 2010. The detection of tumor markers showed elevated serum alpha-fetoprotein (AFP) at 327.6 ng/mL (normal range, 0-10.0ng/mL) and human chorionic gonadotropin (beta-hCG) at 116.1mIU/mL (normal range, 0-5.0 mIU/mL). He underwent a complete surgical tumorectomy, and the histopathology showed a malignant mixed germ cell tumor encompassing seminoma and immature teratoma tumor components (Figure 1A-F). After this resection, the patient recovered well, with significantly decreased AFP (85.4 ng/mL) and normal beta-HCG (1.2 mIU/mL). He was then consolidated with 4 cycles of cisplatin-based chemotherapy concurrent with three-dimensional conformal radiotherapy. A total absorbed dose of 3060 centigrays (cGy) in 17 fractions of 180Gy each was administered to the primary mediastinal lesion, middle and superior mediastinum, and double supraclavicular area. However, at the end of 2014, he experienced the recurrence of GCT with a metastatic lesion located on the posterior basal segment of the lower lobe of the left lung. He then underwent pneumoresection, and the pathological result revealed a single immature teratoma (Figure 1G-I). He subsequently received 6 cycles of consolidated chemotherapy, including vindesine, ifosfamide, and cisplatin. Afterward, the patient remained in a stable remission condition.
At the beginning of 2020, he was urgently admitted to our hospital with 1 day of persistent chest pain and severe fatigue. Clinical symptoms showed a low-grade fever, flushed skin, and splenomegaly. A complete blood cell count showed anemia (hemoglobin: 8.2 g/dL), leukocytosis (15.66*109/L), and thrombocytopenia (38*109/L). Coagulation tests demonstrated a higher D-dimer value (2340 microg/L) and a slightly prolonged activated partial thromboplastin time (37.4 s). The routine chemical analysis detected a high level of lactate dehydrogenase (LDH) (878 U/L) in the peripheral blood. The results of computed tomography scan and transabdominal ultrasound revealed hepatosplenomegaly and seroperitoneum. Positron emission tomography/computed tomography (PET/CT) detected a diffuse increase in systemic bone metabolism and hepatosplenomegaly with slightly increased FDG metabolism, which was consistent with the manifestation of blood system diseases. There was no evidence indicating the second recurrence of GCT.
A peripheral blood smear revealed the existence of 22% MC-like immature cells. BM aspiration showed substantial infiltration (67% of all nucleated cells) from morphologically heterogeneous atypical circles to oblong cells containing abundant cytoplasm with metachromatic coarse granules. Chemical staining results showed that atypical cells were negative for nonspecific esterase (NSE), peroxidase (POX), and naphthol AS-D chloroacetate esterase staining (NAS-DCE), except for toluidine blue staining (Figure 2). An analysis of the BM aspirate via multiparameter flow cytometry revealed that abnormal cells were positive for CD45, CD117, CD13, CD33, and CD9 but weakly positive for CD2 and CD22, and negative for CD16, CD7, kappa, lambda, CD19, CD38, HLA-DR, CD35, CD65, CD15, CD11b, CD123, CD79a, CD10, CD25, CD34, and MPO (Figure 3). The chromosomal G banding analysis showed a normal karyotype (46, XY). 16 myeloid leukemia-associated fusion genes, including MLL-AF6, CBFB-MYH11, AML1-ETO, PML-RARalpha, and BCR-ABL, were negative through reverse transcription-polymerase chain reaction (RT-PCR). In addition, fluorescence in situ hybridization detected that RARalpha rearrangement was negative. Next-generation sequencing (NGS) of the BM aspirate identified stable mutations in TP53 P301Qfs*44, FLT3 R973X, SETBP1 N272D, and JAK3 I688F, whereas KIT mutations were not detected. Their detailed nucleotide alterations and variant allele frequency (VAF) are shown in Table 1. Four mutated genes were sequenced again via Sanger sequencing (Figure 4). The PCR primers that were used are listed in Supplemental Table 1. The bone marrow biopsy revealed atypical cells that were mainly oval and short spindle cells distributed in clusters and eosinophilic by hematoxylin-eosin (HE) staining, accounting for 80% of the nucleated cells. Immunohistochemical staining confirmed positivity for CD117 and negativity for MPO, CD25, and CD34 (Figure 5). 
The patient was first treated with 2 weeks of dexamethasone (10 mg/day for 1 week and then 5 mg/day for 1 week). Surprisingly, his anemia and thrombocytopenia exhibited significant improvements. When confirmed the diagnosis of MCL, the patient was transferred to another hospital for treatment. His following prognosis was further tracked. He was again diagnosed with MCL and treated with the combination therapy of dasatinib (100 mg/day), ruxolitinib (5 mg/bid for the first week and then 10 mg/bid as a maintenance treatment), and dexamethasone (20 mg/day for 1 week and then 10 mg/day for 4 days). After two weeks of treatment, his condition displayed evident remission, particularly a notable decrease in spleen size. Nevertheless, he subsequently died of acute respiratory distress syndrome after undergoing the first cycle of combination chemotherapy with cladribine (9.5 mg d1-5) and cytarabine (1930 mg d1-5). The patient's survival time was 2.4 months after the initial presentation of MCL.