S-100 protein expressing spindle cells in spindle cell lipoma: a diagnostic pitfall

The Rapidly Expanding Group of RB1-Deleted Soft Tissue Tumors: An Updated Review

The classification of soft tissue tumors has evolved considerably in the last decade, largely due to advances in understanding the pathogenetic basis of many of these, sometimes rare, tumors. Deletion of Retinoblastoma 1 (RB1), a well-known tumor suppressor gene, has been implicated in the tumorigenesis of a particular group of soft tissue neoplasms. This group of so-called “RB1-deleted soft tissue tumors” has been rapidly expanding in recent years, currently consisting of spindle cell/pleomorphic lipoma, atypical spindle cell/pleomorphic lipomatous tumor, pleomorphic liposarcoma, myofibroblastoma, cellular angiofibroma, and acral fibromyxoma. Most of these neoplasms, except pleomorphic liposarcoma, are considered benign entities and are mainly described in the older adult population. This article will review the currently known morphological, immunohistochemical, and molecular features of this heterogeneous group of mesenchymal tumors with an emphasis on differential diagnosis.

A contemporary review of myxoid adipocytic tumors

Myxoid adipocytic tumors encompass a broad heterogeneous group of benign and malignant adipocytic tumors, which are typically myxoid (e.g. myxoid liposarcoma, lipoblastoma and lipoblastoma-like tumor of the vulva) or may occasionally appear predominantly myxoid (e.g. pleomorphic liposarcoma, atypical lipomatous tumor, dedifferentiated liposarcoma, chondroid lipoma, spindle cell/pleomorphic lipoma, atypical spindle cell lipomatous tumor and atypical pleomorphic lipomatous tumor). There have been significant advances in recent years in classification and understanding the pathogenesis of adipocytic tumors, based on the correlation of histologic, immunohistochemical, and cytogenetic/molecular findings. Despite these advances, the morphologic diagnosis and accurate classification of a myxoid adipocytic tumor can be challenging due to major morphologic overlap between myxoid adipocytic and non-adipocytic tumors. This article will provide a review on the currently known morphological, immunohistochemical and molecular features of myxoid adipocytic tumors and their differential diagnosis.

Immunohistochemical differentiation between spindle cell lipoma and neurofibroma of oral cavity using CD34 and SOX10

Spindle cell lipoma (SCL), also called as pleomorphic adenoma, is a rare variant of lipoma histopathologically characterized by an admixture of mature fat cells with spindle cells and occasionally mast cells with myxoid connective tissue stroma and thick bends of birefringent collagen. Although buccal mucosa is the most common location for oral lipomas, for SCL, it is an exceedingly rare location. We report a case of an asymptomatic swelling of buccal mucosa that simulated the features of neurofibroma on histopathological examination, and the final diagnosis of SCL was made on the basis of immunohistochemical features. This is the first documentation of oral SCL using SOX10 to achieve the final diagnosis.