Characterization of childhood precursor T‐lymphoblastic lymphoma by immunophenotyping and fluorescent in situ hybridization: A report from the Children's Oncology Group

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Abstract
Background T‐lymphoblastic lymphoma (T‐LBL) accounts for 25–30% of childhood non‐Hodgkin's lymphoma and is closely related to T‐lymphoblastic leukemia (T‐ALL). Recently, we demonstrated distinct differences in gene expression between childhood T‐LBL and T‐ALL, but molecular pathogenesis and relevant protein expression patterns in T‐LBL remain poorly understood. Procedure Children with T‐LBL with disseminated disease were registered and treated on COG protocol 5971. Paraffin‐embedded tumor tissue was obtained at diagnosis for immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) studies. We determined the pattern and intensity of staining for c‐Myc, Skp2, Mib‐1, p53, TCL‐1, bcl‐2, and bcl‐6 proteins by IHC and c‐Myc, p53, bcl‐2, bcl‐6, and TCR α/δ molecular alterations by FISH in 22 pediatric T‐LBL cases. Results The majority of T‐LBL samples expressed Mib‐1 (59%) and c‐Myc (77%) proteins in greater than 50% of the cells, but Skp2 (14%), p53 (14%), and bcl‐2 (23%) expression was less common. FISH studies demonstrated 18% gains and 10% losses in c‐Myc, 16% gains in p53, 12% gains and 6% losses in bcl‐2, and 6% gains and 19% losses in bcl‐6 with little direct correlation between the IHC and FISH studies. Conclusions Childhood T‐LBL is a highly proliferative tumor associated with enhanced expression of c‐Myc protein, but without detectable c‐Myc molecular alterations. FISH studies did not identify consistent etiologies of molecular dysregulation, and future studies with other molecular approaches may be required to elucidate the molecular pathogenesis of childhood T‐LBL. Pediatr Blood Cancer 2008;51:489–494.

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