A rare pediatric case of a thymic cytotoxic and lymphoblastic T/NK cell lymphoma.

Attempts to establish a concise classification of lymphoblastic lymphomas (LBLs) have gained momentum in recent years, mainly due to the expanding possibilities of immunohistochemical and genetic characterization of different disease entities. Thus, cases of immature lymphoid malignancies with unusual immunopathological features have been reported during the last years, suggesting the need for new LBL classification concepts. To further characterize and demonstrate the extended spectrum of LBL, we present an unusual pediatric case of LBL that could not be categorized into one of the subgroups and exhibited a benign course after surgical treatment and subsequent chemotherapy. A mediastinal tumor of a 6-year-old Caucasian boy was examined by clinical staging, light microscopy, immunohistochemistry and PCR assays. The tumor cells reacted with TdT and had a positive cytoplasmic immunoreactivity for CD3. Further T- aand NK-cell markers CD1a, CD4, CD8, CD10, and CD56 reacted positively, but CD57, CD16 and CD 30 (Ber H2) were all negative. CD34 as a marker for bipotential B/T-precursors was also positive. B cell markers (CD20, CD22, Cd79a and IgM) were all negative. No clonal B cell Ig or T cell gamma chain rearrangements were detectable. Epstein Barr virus and other Herpes Virus DNA were not detected using a sensitive PCR assay. The applied chemotherapy was tolerated well and a complete remission of the tumor was achieved (observation period three years after the initial diagnosis). Localization, morphology, and the expressions markers made the tumor a typical member of the LBL group. However, our case represents a rare pediatric lymphoma derived from a thymic precursor committed to T/NK-cell differentiation and a favourable outcome after chemotherapy.