PNET‐like features of synovial sarcoma of the lung: A pitfall in the cytologic diagnosis of soft‐tissue tumors

Abstract

Fine-needle aspiration (FNA) cytology of soft-tissue tumors is evolving. As more experience is gained, we are becoming aware of potential pitfalls. We describe 2 cases of synovial sarcoma of the lung, primary and metastatic, in patients who had FNA biopsy performed on a lung mass. The cytologic smears showed extremely cellular groups of malignant small round cells, intersected by small blood vessels, with numerous loose single cells, in a background of macrophages and mature lymphocytes. The tumors displayed monomorphic cells forming rosettes and displaying occasional mitoses. A diagnosis of neuroendocrine tumor/primitive neuroepithelial tumor (PNET) was suspected. Furthermore, this suspicion was supported by immunohistochemical stains, which showed positivity for a neuroendocrine marker, Leu 7 (case 1), and for a neural marker, CD 99 (O 13 or HBA 71) (both cases); and negativity for cytokeratins (case 1). The resection specimen of case 1 had mostly tightly packed small round cells, with occasional rosettes, similar to the FNA biopsy, and focal areas composed of spindle cells, organized in a focal fibrosarcoma-like and hemangiopericytoma-like pattern. A balanced translocation between chromosomes X and 18, demonstrated by both karyotyping and fluorescent in situ hybridization (FISH), enabled us to make a diagnosis of synovial sarcoma, which was histologically classified as poorly differentiated. Case 2 was a metastatic biphasic synovial sarcoma of the arm, with a prominent epithelial component. Synovial sarcoma, when composed mainly of small round cells on cytologic smears, is a great mimicker of neuroendocrine/PNET tumors, with light microscopic and immunohistochemical overlap. Awareness of this potential pitfall may aid in preventing a misdiagnosis. Its recognition is of major concern, especially for the poorly differentiated variant, because it is associated with a worse prognosis.

Primary Synovial Sarcoma of the Lung with Intra-Cardiac Extension

“…After radiation therapy was given for Hodgkin’s disease, they found a 2.3% excess risk of developing a second malignant neoplasm per year at 15 years of follow-up and a 4% excess risk per year at 20 years [17]. Of the nearly 60 cases reported in literature, only 11 have described the definitive molecular detection of SYT-SSX fusion gene transcription [3,4,5,6,7,8,9,10]. The function of the fusion protein remains uncertain: the SYT protein appears to function as a transcriptional activator, whereas the SSX protein appears to function as a transcriptional co-repressor.…”

“…Although synovial sarcoma has microscopic resemblance to normal synovium, it is differentiated from synovium based upon staining for epithelial markers including cytokeratin or epithelial membrane antigen. Primary pulmonary synovial sarcoma (PPSS) is extremely rare, but the occurrence of this tumor is being increasingly recognized [3,4,5,6,7,8,9,10,11,12]. Herein, we present the first description of primary pulmonary synovial sarcoma with direct intra-cardiac extension.…”

Fine Needle Aspiration Biopsy of Monophasic Spindle Synovial Sarcoma of Lung with Fluorescence in Situ Hybridization Identification of t(x;18) Translocation

“…2 Cytologic descriptions of primary poorly differentiated and biphasic variants as well as metastatic poorly differentiated variants are available. [6][7][8][9] Regarding the role of molecular studies, it has been shown to be helpful most often when the primary location is unusual. When the diagnosis is certain based on combined clinical, histopathologic (biphasic pattern) and immunohistochemical findings, molecular testing is not always necessary.…”

Unusual presentation of poorly differentiated primary pulmonary synovial sarcoma (PD‐PPSS) diagnosed by EBUS‐TBNA with cytogenetic confirmation—A diagnostic challenge

“…4,26,27 Recognition of this subtype of SS is of practical importance mostly due to the diagnostic difficulties it poses and due to its more aggressive behavior.…”

“…4 Although the use of the diagnosis "poorly differentiated" SS should be restricted to mostly cases in which a reasonably large amount of tissue is available for examination, which would allow the exclusion of the classic morphologic patterns, the term has been previously used in the cytology literature for cases composed predominantly of small round cells resembling Ewing sarcoma. 26,27 The cytologic features of poorly differentiated SS have been described previously. ard" for this diagnosis in problematic cases.…”