Cytomorphological spectrum, including immunohistochemical results of 16 cases of clear cell sarcoma of soft tissue, along with positive EWSR1 gene rearrangement result in two cases.

OBJECTIVES: To describe the cytopathological features of clear cell sarcomas (CCSs), including immunohistochemical and molecular results, the latter in selected cases. METHODS: Sixteen consecutively diagnosed cases of CCS of soft tissue, over 6-year duration were included. Fine needle aspiration cytology was performed for primary diagnosis in three and for recurrent/metastatic lesions in 12 cases. Cytopathological features in 16 cases (conventional Papanicolaou- and May-Grünwald Giemsa-stained smears) were critically analysed. Corresponding histopathological and immunostained sections were available in 15 cases. Two cases were tested for EWSR1 gene rearrangement by fluorescence in-situ hybridisation. RESULTS: Sixteen tumours occurred in patients with age ranging from 18 to 56 years (median = 33.5); M: F ratio = 1:1; in deep soft tissues, mostly in extremities. Primary cytopathological diagnosis (3 cases) was CCS with a differential diagnosis of melanoma (1 case) and poorly differentiated malignant tumour (2 cases). On review, smears were predominantly hypercellular (n = 14), invariably composed of monomorphic appearing epithelioid/polygonal cells (n = 16), including spindle cells (n = 6); mostly singly scattered (n = 16), in loose clusters (n = 12); with prominent nucleolisation (n = 16); granular to vacuolated, well-defined cytoplasm (n = 12), binucleation/multinucleation (n = 9); mitoses (n = 6); sudden anisonucleosis; racquet-shaped cells (n = 3), against a tigroid background (n = 2), along with focal intracytoplasmic pigment deposition (n = 2). Immunohistochemically, tumour cells were positive for S-100P (15/15), HMB-45 (15/15) and melan-A(6/12). Two cases tested for EWSR1 rearrangement displayed red-green split signals. CONCLUSIONS: This constitutes one of the largest series describing the cytomorphological spectrum of CCS of soft tissue. Certain features, such as singly scattered monomorphic, epithelioid cells with prominent nucleolisation are useful diagnostic clues. Immunohistochemical stains are necessary and molecular testing is further helpful in reinforcing a diagnosis in certain cases. A correct diagnosis has crucial treatment implications.

Identification of a self-association domain in the Ewing's sarcoma protein: a novel function for arginine-glycine-glycine rich motifs?

The Ewing's sarcoma (EWS) protein is a ubiquitously expressed RNA chaperone. The EWS protein localizes predominantly to the nucleus. Previous reports have suggested that the EWS protein is capable of dimerizing. However, to date this has not been confirmed. Here, using a novel panel of recombinant proteins, we have performed an in vitro biomolecular interaction analysis of the EWS protein. We have demonstrated that all three arginine-glycine-glycine (RGG) motifs are capable of binding directly to the survival motor neuron protein, a Tudor domain containing EWS binding partner. We have also confirmed EWS is capable of self-associating, and we have mapped this binding domain to the RGG motifs. We have also found that self-association may be required for EWS nuclear import. This is the first direct evidence of RGG domains being involved in self-association and has implications on all RGG-containing proteins.