Abstract
Spindle cell rhabdomyosarcoma is a rare subtype of rhabdomyosarcoma mainly seen in children. Occasional aberrant staining with a variety of immunohistochemical markers has been noted. The aberrantly expressed markers include alpha-smooth muscle actin, cytokeratin, S100, neurofilaments, CD20, immunoglobins, and CD117. We report herein two pediatric cases displaying strong CD34 positivity and one with additional focal CD117 positivity, causing considerable difficulty in distinction from solitary fibrous tumor and extra-gastrointestinal stromal tumor. To our knowledge, CD34 staining has been merely reported in rhabdomyosarcoma. Spindle cell rhabdomyosarcoma has to be considered in the differential diagnosis of childhood spindle cell tumors. Post-chemotherapy specimens should be evaluated in caution, since chemotherapy can cause considerable changes in tumor antigen expression. Since CD117 and CD34 are stem cell markers, their positivity in pediatric tumors should be interpreted with caution. Even if the morphology is not supportive, a wide immunohistochemical panel should be applied in childhood malignant solid tumors.
Highlights
Spindle cell rhabdomyosarcoma (SCRMS) is a rare subtype of rhabdomyosarcoma (RMS) mainly seen in children and accounting for 3-4.4% of all RMS subtypes [1]
We report two cases displaying diffuse CD34 positivity and one with additional focal CD117 positivity, resulting in confusion with solitary fibrous tumor (SFT) and extra-gastrointestinal stromal tumor (GIST) and causing considerable difficulty in diagnosis
A tru-cut biopsy revealed a mitotically active spindle cell tumor that was positive for desmin and vimentin and negative for alpha-smooth muscle actin, epithelial membrane antigen (EMA) and leukocyte common antigen (LCA)
Summary
Spindle cell rhabdomyosarcoma (SCRMS) is a rare subtype of rhabdomyosarcoma (RMS) mainly seen in children and accounting for 3-4.4% of all RMS subtypes [1]. We report two cases displaying diffuse CD34 positivity and one with additional focal CD117 positivity, resulting in confusion with solitary fibrous tumor (SFT) and extra-gastrointestinal stromal tumor (GIST) and causing considerable difficulty in diagnosis. It is hoped that this case report will expand the literature on pediatric SCRMS and alert pathologists to the possible diagnostic challenge of distinguishing between SCRMS and its spindle cell mimics and the relatively frequent expression of CD34 in childhood tumors.
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