Precursor B lymphoblastic lymphoma presenting as lytic bone lesions

Precursor B lymphoblastic lymphoma is an aggressive but potentially curable disease. This lymphoma most often manifests in the skin and lymph nodes an d, less commonly, as lytic bone lesions. In the! bone, this lymphoma must b e differentiated from small round blue cell tumors, diffuse large B-cell ly mphoma and acute myelogenous leukemia We describe the morphologic and immun ophenotypic features in 4 patients, 2 children, 1 teenager and 1 adult, who initially presented with bone pain and osteolytic lesions but without peri pheral blood or iliac bone marrow involvement, Positive immunohistochemical staining of the neoplastic cells was observed for anti-CD10 (3/4), CD20 (3 /4), CD34 (1/4), CD43 (4/4), CD45/CD45RB (2/4), CD79a (4/4), CD99 (MIC2) (2 /4), and terminal deoxynucleotidyl transferase (4/4). CD3 was absent in all cases. Immunophenotyping these neoplasms is essential to establish the cor rect diagnosis of precursor B lymphoblastic lymphoma, and a panel of antibo dies is required because of the immunophenotypic heterogeneity.