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* Context.--A number of fibro-osseous and osteocartilaginous lesions, especially common in the small bones of the hand and feet, pose a diagnostic challenge and have historically been thought to be reactive lesions. However, modern molecular techniques when supplementing clinical, radiographic, and histologic evaluation suggest they may, in fact, be neoplasms. Objective.--To review the clinical presentation and histopathologic, molecular, and radiologic features of selective bone lesions, focusing most specifically on subungual exostosis, florid reactive periostitis, and bizarre periosteal osteochondromatous proliferation. Data Sources.--Literature review and personal experience are the sources of this review. Conclusions.--Some lesions previously thought to be reactive are locally aggressive and demonstrate reproducible molecular abnormalities, and thus may be neoplasms. Although most common in the bones of the fingers and toes, these lesions also occur in long and other bones. The clinical presentations, radiologic appearances, and histopathologic features often overlap, making the diagnosis challenging, and these lesions may require molecular evaluation to maximize accurate prognostication., Subungual exostosis (SE), florid reactive periostitis (FRP), and bizarre parosteal osteochondromatous proliferation (BPOP) are benign lesions that commonly arise from the small trabecular bones of the hands and feet in [...]

* Context.--Small round cell tumors of soft tissue and bone constitute a divergent group of neoplasms. These lesions often demonstrate overlapping clinical and radiologic characteristics and share histomorphologic and sometimes immunophenotypic similarities, but they typically have diverse prognostic outcomes, thus warranting different clinical management. Recent advances in molecular and cytogenetic techniques have identified a number of novel molecular alterations contributing to the diversity of these lesions. This state-of-the-art knowledge has enhanced our understanding of these diseases. Objective.--To provide an overview of the current concepts in the classification and diagnosis of small round cell tumors of soft tissue and bone, focusing on salient histologic features, key immunophenotypic characteristics, and recent molecular genetic advancements. Data Sources.--Data were obtained from pertinent peer-reviewed English-language literature and firsthand experience from the authors as practicing bone and soft tissue pathologists. Conclusions.--Immunohistochemistry plays a vital role in rendering a specific diagnosis or narrowing the differential diagnosis in small round cell tumors of soft tissue and bone. Molecular genetic studies are often needed, especially for those lesions with unusual histologic features, an uncommon immunoprofile, and/or unusual clinical presentation. Accurate diagnosis of these tumors necessitates recognition of salient histologic features, judicious and astute use of ancillary studies, and correlation with the clinical and radiologic characteristics to guide clinical decision-making., Small round cell tumors (also known as small, blue, round cell tumors) constitute a divergent group of neoplasms. These tumors are morphologically alike and characterized as highly aggressive malignant tumors [...]