Primary cutaneous pre-B lymphoblastic lymphoma immunohistologically mimics Ewing's sarcoma/primitive neuroectodermal...

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.