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Sirtuin, silent mating-type information regulation 2 homolog Saccharomyces cerevisiae 1 (SIRT1), is a protein that has been implicated in multiple mammalian functions including cell aging, stress resistance, and differentiation. SIRT1 has also been shown to be involved in multiple tumors. In addition, new pharmacotherapies have recently been approved that target SIRT1. The purpose of this study was to use immunohistochemistry to characterize SIRT1 protein expression in human soft tissue neoplasms with the hopes of finding new diagnostic and therapeutic modalities. SIRT1 immunoreactivity was reviewed in a series of 164 soft tissue tumors including alveolar soft part sarcoma, angiomyolipoma, clear cell sarcoma, desmoid/fibromatosis, desmoplastic small round cell tumor, Ewing sarcoma, gastrointestinal stromal tumor, glomus tumor, leiomyoma, leiomyosarcoma, lipoma, liposarcoma, malignant peripheral nerve sheath tumor, nodular fasciitis, osteosarcoma, rhabdomyosarcoma, schwannoma, solitary fibrous tumor, synovial sarcoma, undifferentiated pleomorphic sarcoma, and Wilms tumor. In addition, numerous benign tissues were tested for SIRT1 reactivity. In nonneoplastic tissue, strong cytoplasmic SIRT1 reactivity was observed in all prostate stroma, smooth muscle, and striated muscle. A similar pattern of cytoplasmic SIRT1 expression was observed in soft tissue neoplasms with myoid differentiation, namely, angiomyolipoma (100%), glomus tumor (100%), leiomyoma (90%), leiomyosarcoma (76.5%), and rhabdomyosarcoma (87%). The other lesions examined were negative. Although the physiologic role of SIRT1 remains to be clarified in myoid tissues and neoplasms differentiating along these lines, this observation points to a potential role for this marker in diagnostic immunohistochemistry. Furthermore, the recent emergence of drugs capable of selectively inhibiting SIRT1 raises the possibility of a potential application for targeted therapy. Additional studies are necessary to further characterise the role of SIRT1 in myoid tissues and neoplasms. [ABSTRACT FROM AUTHOR]

PEComas are mesenchymal neoplasms composed of perivascular epithelioid cells (PEC) and include a spectrum of tumors. PEComas and malignant melanoma share common morphological, immunohistochemical, and ultrastructural features, such as epithelioid cell morphology and melanocytic immunophenotype. Melanocytic markers commonly expressed in PEC tumors include HMB-45, Melan-A/MART-1, tyrosinase, microphthalmia transcription factor (MITF), and occasionally, S100. Given this morphological and immunophenotypical overlap, the differential diagnosis between a PEComa and malignant melanoma can represent a challenge. Additional diagnostic difficulty is the differentiation of melanoma and PEComa from clear cell sarcoma that is indistinguishable from melanoma based on the immunohistochemical profile. Recent studies have shown that MUM-1, a known lymphocyte marker shows positive immunostaining in nevi and melanomas, its expression in PEComas and clear cell sarcoma, however, has not been previously addressed. In this study, the authors analyzed MUM-1 expression using immunohistochemistry in PEComas (n = 8), the PEComa family members, angiomyolipomas (n = 13), and clear cell sarcomas (n = 11) and compared the staining pattern with malignant melanomas (n = 25), both primary (n = 14) and metastatic (n = 11). It was found that 92.3% of primary melanomas and 81.3% of metastatic melanomas were MUM-1 positive. In contrast, MUM-1 was only weakly positive in only 25% of PEComas and negative in all angiomyolipomas. MUM-1 expression was noted in 72.7% of clear cell sarcomas. The study demonstrated differential MUM-1 expression between PEComas and other true melanocytic tumors and suggested that the addition of MUM-1 to the usual panel of melanocyte markers could be a helpful adjunctive study to aid in the differential diagnosis between these entities. [ABSTRACT FROM PUBLISHER]

The DNA-binding factor TFE3 is closely related to microphthalmia-associated transcription factor (MiTF) and is over-expressed in alveolar soft part sarcoma (ASPS) and select renal cell carcinomas. Reports of TFE3 expression in PEComa prompted investigation into TFE3 expression among other members of the putative MiTF group of neoplasms. The authors examined cases of PEComa (n = 6), conventional angiomyolipoma (AML; n = 22), metastatic melanoma (n = 16), and clear cell sarcoma (CCS; n = 9) for TFE3 expression. Nuclear immunostaining was observed in 74% (39/53) of cases, as follows: 5/6 PEComas, 18/22 AMLs, 10/16 metastatic melanomas, and 6/9 CCSs. However, with the exception of PEComas, compared with ASPS controls, TFE3 staining was significantly less intense in the tumors examined. These results illustrate that TFE3 immunoreactivity is detectable in other members of the MiTF family of neoplasms. For this reason, such neoplasms warrant consideration in the differential diagnosis with nuclear TFE3 immunoreactivity, particularly when staining is focal and less intense. [ABSTRACT FROM PUBLISHER]

The vast majority of soft tissue tumors (STT), especially sarcomas, should be examined according to a national standard for pathologic evaluation, including a national consensus on a grading system and elements of a synoptic pathology report. The margins should be separated into fascial margins and other surgically cut margins. If questions about the diagnosis arise, a second opinion should be sought from an expert in sarcoma pathology. Whenever possible, tissue should be frozen for potential molecular diagnosis and additional tissue banked for research. Finally, there is a need for a national registry for rare sarcoma types. [ABSTRACT FROM AUTHOR]