Childhood ALL masquerading as Ewing's sarcoma

Abstract

21516 Background: Lymphoma of the pelvic bone can be confused radiologically and morphologically with Ewings sarcoma (EWS). Immunohistochemistry: FLI-1, CD99, CD20, and CD45 can discriminate these entities. Precursor B cell acute lymphoblastic leukemia (ALL) presenting as a destructive bony mass mimicking EWS has not been previously reported and cannot be discriminated from EWS by these stains. The objective of this report is to describe a case of ALL that mimicked EWS clinically and pathologically. Methods: A 7 yr old boy presented with limping and a large iliac mass. MRI showed a 10× 4cm mass with cortical destruction. Biopsy showed small round blue cells, positive for CD99 and FLI-1 and negative for CD45, CD20 and synaptophysin. The pathologist stated the ‘diagnosis of Ewing's sarcoma is secure.’ Labs showed: WBC = 8,300, Hg = 10.0, platelets = 48,000, and LDH = 680. CT showed mild splenomegaly. A bone marrow biopsy distant from the mass was ‘packed’ with blue cells. Results: Flow cytometry was positive for: CD34, HLA-DR, CD22, CD10 and CD19, and negative for: CD 45 and CD20; while immunohistochemistry was positive for: CD10, CD22, TdT, CD99 and FLI-1 and negative for CD20 and CD45 in all biopsies. F.I.S.H. was negative for: t(11:22), t(9;22), t(12;21), (11q23) and t(8;14). These findings are diagnostic of acute precursor B-cell ALL. Seven days after starting chemotherapy for ALL, the mass vanished and the patient has remained in remission since. CT normalized in 5 months. Conclusion: All biopsies initially stained in a characteristic pattern for EWS and against lymphoma. However this pattern is also seen in pre-B cell ALL (Table 1). Pre-B cell ALL can present as an isolated destructive bony mass, clinically and pathologically consistent with EWS. Attention to the CBC and addition of CD10 and CD22 immunohistochemical stains can uncover the diagnosis of ALL masquerading as EWS. Classic Immunohistochemistry for Bone Tumors, B Cell Lymphoma, and Pre-B Cell Leukemia Marker EWS Lymphoma Pre B Cell Leukemia FLI-1 Positive Negative Positive CD 99 Positive Negative Positive CD 45 Negative Positive Negative CD 20 Negative Positive Negative CD 10 Negative Negative Positive CD 22 Negative Negative Positive No significant financial relationships to disclose.