Rhabdomyosarcoma

To the Editor.-We read with interest the case report by Douglas Kahn, MD, in the April 1998 issue of the ARCHIVES1 This phenomenon is well-- recognized in pediatric pathology, and it often presents the diagnostic dilemma described in the case report.

We agree with the necessity of performing ancillary studies to avoid a misdiagnosis of acute leukemia, as suggested by Dr Kahn, but our recent experience with several unusual cases of rhabdomyosarcoma would caution against an absolute reliance on immunohistochemistry. As detailed in our recent report,2 rhabdomyosarcomas may on occasion express markers more typical of lymphoid cells. The 3 pediatric tumors that we described were all initially diagnosed as lymphoma/leukemia because of the presence of undifferentiated cells that expressed CD19, CD20, and light-chain restriction. It was not until subsequent cytodifferentiation of these neoplasms following chemotherapy did the true nature of these lesions become evident. We would thus urge readers also to consider cytogenetic or electron microscopic results in diagnosing unusual bone marrow malignancies.

DAVID M. PARHAM, MD Department of Pathology University of Arkansas for Medical Sciences and Arkansas Children's Hospital Little Rock, Ark

ALFREDO PINTO, MD Department of Laboratories Alberta Children's Hospital Calgary, Alberta, Canada GIOVANNI TALLINI, MD Department of Pathology Yale University School of Medicine New Haven, Conn

ROBERT W NOVAK, MD Department of Pathology Childrens Hospital Medical Center Akron, Ohio

1. Kahn DG. Rhabdomyosarcoma mimicking acute leukemia in an adult: report of a case with histologic, flow cytometric, cytogenetic, immunohistochemical, and ultrastructural studies. Arch Pathol Lab Med. 1998;122:375-378.

2. Pinto A, Tallini G, Novak RW, Bowen T, Parham DM. Undifferentiated rhabdomyosarcoma with lymphoid phenotype expression. Med Pediatr Oncol. 1997;28:1 65-170.

In Reply.-The comments and reference provided by Dr Parham et al are appreciated. They highlight additional difficulties in making the diagnosis of rhabdomyosarcoma.

Unlike my case,1 where flow cytometry indicated a myeloid differentiation of a small round-cell tumor, all 3 of their cases were stained with lymphoid markers, either with flow cytometry or in tissue sections.2 In 1 of their cases, a clue to the diagnosis of rhabdomyosarcoma was the cytologic appearance of the neoplasm, including periodic acid-Schiff-positive vacuoles in the cytoplasm and phagocytosis by tumor cells. Furthermore, after treatment with chemotherapy, examination of additional pathologic material demonstrated clearly identifiable rhabdomyoblasts. The increase in cytoplasm after treatment was a feature noted in my case as well. One of their tumors was negative for desmin, alpha-smooth muscle actin, and myoglobin. Another patient's neoplasm was negative for desmin as well, and the third neoplasm was positive for muscle-specific actin. After the diagnosis of rhabdomyosarcoma was made in 2 of their cases, the tumors in a retrospective analysis exhibited positive staining with MyoD1 antibodies. In 2 cases, the rhabdomyosarcoma showed the characteristic translocation (2;13), one with q36;q14 and the other with q37;q14, which was similar to my case. Cytogenetic analysis revealed no metaphases in the first sample in one case. However, Parham et al also identified a study demonstrating the nonspecific nature of the translocation (2;13), as this abnormality had been identified in B-cell prolymphocytic leukemia.3 In 1 case, electron microscopy was not performed. Electron microscopy was performed in the other 2 cases; one case failed to demonstrate evidence of muscle differentiation, and in the other the diagnosis of rhabdomyosarcoma was confirmed after chemotherapy.

On a final note, the patient has since died of his disease.

DOUGLAS G. KAHN, MD Consolidated Laboratory Services Van Nuys, CA 91406

1. Kahn DG. Rhabdomyosarcoma mimicking acute leukemia in an adult: report of a case with histologic, flow cytometric, cytogenetic, immunohistochemical, and ultrastructural studies. Arch Pathol Lab Med. 1998;122:375-378.

2. Pinto A, Tallini G, Novak RW, Bowen T, Parham DM. Undifferentiated rhabdomyosarcoma with lymphoid phenotype expression. Med Pediatr Oncol. 1997;28:165-170.

3. Adami F, Sancetta R, Trentin L, Semenzato G, Stella M. The pediatric rhabdomyosarcoma translocation (2;13)(q35;q14) in B-prolymphocytic leukemia. Leukemia. 1993;7:1676-1678.

Copyright College of American Pathologists Dec 1998
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