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Simple Summary: Atypical spindle cell/pleomorphic lipomatous tumor (ASCPLT) is a novel entity of benign adipocytic neoplasm that can show variable CD34 immunoreactivity, loss of Rb expression, and RB1 gene deletion. Due to the rarity of the disease, ASCPLT remains poorly understood. This review aims to provide a comprehensive reference, offer valuable insights into the clinicopathological characteristics and pathogenesis, and discuss the differential diagnosis of ASCPLT. Atypical spindle cell/pleomorphic lipomatous tumor (ASCPLT) is a rare and recently described adipocytic neoplasm that primarily occurs in the subcutis of the limbs and limb girdles, particularly of middle-aged adults. It has locally recurrent potential if incompletely excised but no risk for distant metastasis. ASCPLT is histologically similar to spindle cell/pleomorphic lipoma and atypical lipomatous tumor and shows a mixture of atypical spindle cells, adipocytes, lipoblasts, floret-like multinucleated giant cells, and/or pleomorphic cells. It has been recently recognized that ASCPLT can undergo sarcomatous transformation. However, the biological significance of morphological sarcomatous transformation in ASCPLT remains uncertain. Immunohistochemically, the tumor cells show variable expression of CD34, S-100 protein, and desmin. Loss of nuclear Rb expression is observed in the majority of cases. ASCPLT lacks MDM2 gene amplification but can show RB1 gene deletion in a significant subset of cases. Complete surgical excision is the treatment of choice. This review provides an overview of the current knowledge on the clinicoradiological features, pathogenesis, histopathology, and treatment of ASCPLT. In addition, we will discuss the differential diagnosis of this new entity. [ABSTRACT FROM AUTHOR]

Background/aim: Desmoplastic fibroblastoma, also known as collagenous fibroma, is a rare benign mesenchymal neoplasm that primarily arises in the subcutaneous tissue of upper extremities and limb girdles. The knee is an uncommon location for desmoplastic fibroblastoma. Recent studies have demonstrated the presence of immunoreactivity for FOS like 1 (FOSL1) and rearrangements of FOSL1., Case Report: A 70-year-old woman presented with a 1-year history of a palpable mass in the medial aspect of the right knee. Physical examination revealed a 4-cm, elastic hard, mobile, nontender mass. Magnetic resonance imaging (MRI) showed a well-defined mass with prominent low signal intensity on all pulse sequences. Contrast-enhanced MRI demonstrated mild internal enhancement with rim enhancement. After an open biopsy, the lesion was successfully treated by complete excision. Histologically, the tumor was composed of bland spindle or stellate-shaped cells embedded in an abundant collagenous stroma. Immunohistochemically, the tumor cells showed diffuse nuclear positivity for FOSL1. These findings were consistent with a diagnosis of desmoplastic fibroblastoma. The patient was asymptomatic and there was no evidence of local recurrence eight months after surgery., Conclusion: Desmoplastic fibroblastoma is a distinctive benign soft-tissue tumor with FOSL1 immunoreactivity and should be clearly distinguished from more biologically aggressive mesenchymal neoplasms., Competing Interests: The Authors declare no conflicts of interest associated with this article., (©2024 The Author(s). Published by the International Institute of Anticancer Research.)

Background/aim: Giant cell tumor of bone (GCTB) is a locally aggressive neoplasm that typically occurs in the ends (epiphyses) of long bones of young adults. Flat bones are uncommon sites of involvement. Herein, we describe an unusual case of pathologically proven GCT of the acromion., Case Report: The patient was a 39-year-old woman with no history of trauma who presented with a 3-month history of right posterior shoulder pain. Physical examination revealed mild swelling and tenderness in the posterior aspect of the right shoulder. Plain radiograph showed a purely lytic lesion, suggestive of a bone tumor. Computed tomography demonstrated an intraosseous lytic lesion with associated cortical thinning and lack of periosteal reaction. On magnetic resonance imaging, the lesion exhibited slightly higher signal intensity compared to skeletal muscle on T1-weighted sequences and heterogeneous high signal intensity on T2-weighted sequences. Strong enhancement was observed following gadolinium administration. The lesion was treated by extensive curettage with adjuvant therapy comprising ethanol and the remaining cavity was filled with polymethylmethacrylate bone cement. Histologically, the lesion was composed of round or spindle-shaped mononuclear cells admixed with numerous osteoclast-like giant cells. Immunohistochemically, the mononuclear neoplastic cells were diffusely positive for H3.3 G34W. The patient was asymptomatic and there was no evidence of local recurrence or distant metastasis 5 months after surgery., Conclusion: Although rare, acromial GCTB should be considered in the differential diagnosis of posterior shoulder pain, especially in young and early middle-aged adults., (Copyright © 2024, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)