Sirtuin 1 (SIRT1): a potential immunohistochemical marker and therapeutic target in soft tissue neoplasms with myoid differentiation.

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.