[Mediastinal T lymphoblastic lymphoma/leukemia: clinicopathological and prognostic analyses of 61 cases]

Objective: To investigate the clinicopathologic features and prognosis of mediastinal T lymphoblastic lymphoma/leukemia (T-LBL/ALL). Methods: Sixty-one patients with mediastinal T-LBL/ALL diagnosed at First Affiliated Hospital of Zhengzhou University from August 1, 2011 to December 31, 2018 were enrolled. Their clinical, pathological, imaging features and prognosis were retrospectively analyzed. Results: Of the 61 patients with mediastinal T-LBL/ALL, 46 were male and 15 were female, with a male to female ratio of approximately 3∶1, aged 5 to 71 years (median 24 years, average of 24.5 years). Radiological findings were mediastinal soft tissue masses (58 cases) or mediastinal multiple enlarged lymph nodes (1 case). The tumor had a diameter of 4.9 to 18.3 cm in size, and data of 2 cases was unavailable. The patient's main symptoms were superior vena cava syndrome (cough, dyspnea, facial or neck edema), shortness of breath and chest pain, while about 1/3 of patients developed B symptoms (high fever, night sweats or significant weight loss). All 61 cases were biopsy specimens, and 2 of the tumors were later resected. Histopathologic examination showed that the thymic tissue epithelial network structure was destroyed or completely disappeared. A large number of lymphocytoid tumor cells were diffusely infiltrative, with infiltration into adipose tissue, starry sky phenomenon, linear-like arrangement, interstitial collagen hyperplasia and tumor cell extrusion. Focal tumor necrosis was present in some cases. Tumor cells were overall small to medium in size. They had little cytoplasm, slightly distorted, round or oval-shaped nuclei, fine chromatin, and innocuous/small nucleoli. Immunohistochemical studies showed that the tumor cells expressed CD7 (100%, 33/33), TDT (93.4%, 57/61), CD99 (83.3%, 25/30), CD1a (4/7), CD10 (8/18), CD34 (13.2%, 5/38), but did not express B cell markers (CD20 and PAX5) or granulocyte monocyte marker (MPO). The Ki-67 proliferation index was usually greater than 50%. One case was tested for TCR clonal rearrangement, which was positive. Several hemotherapy regiments were used. Hyper-CVAD (cyclophosphamide, vindesine, dexamethasone, and epirubicin) were most frequently administrated (60.4%, 32/53), followed by BFM-90 (50.9%, 27/53). Some patients were treated with the above two and other treatment options. Follow-up data were available in 55 of the 61 patients, and 26 patients (47.3%) survived. The average five-year survival rate was 50.6%. The patient's prognosis was not significantly related to the International Prognostic Index, age of onset, gender, or tumor size. Conclusions: The mediastinal T-LBL/ALL is rare, and most of its specimens are needle biopsies. The histological morphology is often difficult to interpret, while the addition of clinical features and immunohistochemistry may help. The combination of CKpan, TDT, CD99, CD7, CD3, PAX5, CD34, CD10, and Ki-67 immunohistochemicl studies may assist in diagnosis of the most cases.