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The clinical evolution and biology of granular cell tumors (GCT) are poorly understood and treatment remains an issue of discussion. The majority of GCT are benign, although some display malignant behavior. The distinction between benign, atypical, and malignant GCT is controversial due to morphological and immunohistochemical overlap and lack of consistent histological and phenotypic criteria that predict behavior. Although histological criteria may indicate increased risk of malignant evolution, some GCT with evident benign appearance exceptionally progress towards metastatic disease. In this review, we discuss current knowledge on GCT, including histologic, immunophenotypic, and molecular characteristics and differential diagnosis. We focus on the following problematic items in GCT: (1) evolution of classification, (2) neural versus non-neural GCT, (3) neoplastic versus reactive disease, (4) malignant transformation of benign GCT, and (5) multiple versus metastatic GCT. We conclude that although a Ki-67 index >10 % and the presence of mitoses and/or of necrosis are frequently associated with malignant behavior, metastasis remains the only unequivocal sign of malignancy in GCT. An infiltrative growth pattern and vascular and/or perineural invasion are not indicative of malignancy. GCT with atypical/uncertain features almost never metastasize, and many of these tumors either behave in a benign fashion or only recur locally (similar to incompletely excised benign tumors). We therefore propose that classical and atypical histological variants form a single group of GCT. GCT with various unfavorable histological features might be labeled as "GCT with increased risk of metastasis" rather than malignant GCT.

The present study describes a new case of EWSR1-negative undifferentiated sarcoma with CIC/DUX4 gene fusion. This case is similar to tumors described as primitive undifferentiated round cell sarcomas that occur mainly in the trunk and display an aggressive behavior. To our knowledge, this is the first report of such a tumor presenting locoregional lymph node metastasis. In view of previous studies that prove the existence of a particular variant of undifferentiated sarcoma with Ewing-like morphology and CIC/DUX-4 gene fusion, a search for this gene fusion in all undifferentiated round cell sarcomas should be considered if a conclusive diagnosis cannot be reached following other conventional studies. Although additional cases with more extensive follow-up studies are needed, we believe that EWSR1-negative undifferentiated small round cell sarcoma with CIC/DUX4 gene fusion should be added to the list of new sarcoma variants with the possibility of lymph node metastasis.

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Breast implant-associated anaplastic large cell lymphoma (ALCL) is a newly described clinical and pathologic entity that typically presents as seroma in the fibrous scar around the implant. Less frequently, it presents as a solid peri-implant mass, and there have been no reports to date of cutaneous lesions as the presenting manifestation. We report the case of a 56-year-old woman with a history of bilateral breast reconstruction following breast cancer of the right breast who consulted with several papules on the right breast suggestive of metastasis. Histopathology showed a proliferation of large epithelioid lymphocytes with highly pleomorphic cells and nuclei. The neoplastic cells were CD15 and CD30 positive and ALK-1 negative. The epithelial markers were all negative except for epithelial membrane antigen (EMA), which was weakly positive. Molecular analysis showed monoclonal T-cell receptor γ gene rearrangement, confirming a diagnosis of breast implant-associated ALCL. The non-specific morphology of the skin lesions, the epithelioid nature of the neoplastic cells and the expression of EMA can lead to an erroneous diagnosis of skin metastases from a poorly differentiated adenocarcinoma of the breast. We recommend immunohistochemical staining for CD30 and ALK-1 for patients with breast implants who develop anaplastic lesions.