Precursor B-cell lymphoblastic lymphomas (B-LBLs) are rare and most often 
involve the skin in the head and neck region. Histologically, cutaneous B-LBLs 
may be confused with other small round-cell neoplasms. Moreover, half of B-LBL 
patients are negative for CD45 (leucocyte common antigen, LCA), a widely used 
marker for the diagnosis of lymphoma, and a significant portion express CD99, a 
marker for Ewing's sarcoma (ES) or primitive neuroectodermal tumor (PNET). 
Therefore, an extranodal B-LBL may be misinterpreted as PNET or ES. Here, we 
report on 2 boys, aged 10 and 5 years, with primary cutaneous B-LBL of the 
scalp. PNET was initially misdiagnosed because the tumor cells were negative for 
CD45 but strongly positive for CD99. Advanced stage of acute lymphoblastic 
leukemia (ALL) developed later and both patients died during the course of 
treatment for ALL. In retrospective analyses, tumor cells in the initial biopsy 
specimens of both patients were found to be reactive to terminal 
deoxynucleotidyl transferase (TdT), CD43 and CD10. Thus, the diagnosis of B-LBL 
was confirmed. These cases illustrate the possibility that primary cutaneous 
B-LBL may mimic ES or PNET immunophenotypically, and that correct diagnosis in 
doubtful cases may be facilitated by analysis using a complete panel of 
antibodies, particularly including TdT and CD43.