Spindle Cell/Sclerosing Rhabdomyosarcoma
Microscopic Features of Sclerosing Rhabdomyosarcoma: The dominant feature of the tumor is abundant, hyalinized stroma within which the tumor cells are arranged in lobules, nests, microalveoli, or a single file pattern. The stroma may be eosinophilic or basophilic and can resemble osteoid or chondroid matrix. Some cases are hypercellular with minimal stroma and they may be confused with solid variant of alveolar RMS (such as the case shown here). The tumor cells are round or oval with scant eosinophilic cytoplasm, irregular nuclei with coarse chromatin, and one or more nucleoli. Multinucleated giant cells with wreath-like nuclei (seen in alveolar RMS) as well as rhabdomyoblasts with cross-striations are rare. Immunohistochemistry: MyoD1 is usually strongly positive but may be present focally or even absent. Desmin shows focal and dot-like positivity, which is different from the pattern seen in other types of RMS.