[78] Aneurysmal Bone Cyst with Dual Rearrangements of SS18 and USP6

KB Geiersbach, LS Rector, A Hooker, LJ Layfield, ST South. University of Utah School of Medicine, Salt Lake City, UT; ARUP Laboratories, Salt Lake City, UT

Background: Aneurysmal bone cyst (ABC) is a benign osteolytic lesion containing hemorrhagic cystic regions surrounded by a heterogeneous mixture of mesenchymal cells. Rearrangements of the USP6 (also known as TRE2 or TRE17) oncogene are present in approximately 70% of lesions classified as aneurysmal bone cyst. We report a case of a 30 year old woman with a right scapular bone cyst, with classic histologic features of an aneurysmal bone cyst and simultaneous rearrangements of the SS18 (also known as SYT) and USP6 gene loci.
Design: Biopsy tissue was submitted to the pathology laboratory for histologic evaluation, and a portion of fresh tumor was submitted for cytogenetics. RT-PCR for the SS18-SSX1 and SS18-SSX2 translocations was performed on FFPE tissue. FISH analysis for SYT (SS18) was performed on cultures and FFPE sections. FISH analysis for USP6 was performed on FFPE sections using selected bacterial artificial chromosome (BAC) clones flanking the USP6 gene. BAC clones were labeled with Spectrum Green (telomeric) and Spectrum Orange (centromeric) and probe localization was confirmed on normal peripheral blood metaphase cells prior to analysis by fluorescence microscopy.
Results: The resected lesion had classic histologic features of aneurysmal bone cyst. Cytogenetic analysis was performed and showed a complex karyotype: 45,t(X;18;4)(p11.2;q11.2;q13),del(8)(p21),-13,add(17)(p11.2) in twenty cells analyzed. A rearrangement of SS18 was observed in 78% of interphase cells by fluorescence in situ hybridization (FISH) on cultured material. RT-PCR for the SS18-SSX1 and SS18-SSX2 translocations showed no evidence of the X;18 translocation associated with synovial sarcoma. FISH analysis on areas of tumor from FFPE tissue sections showed a rearrangement of SS18 in 25% of nuclei and a rearrangement of USP6 in 24% of nuclei.
Conclusions: We describe a dual rearrangement of SS18 and USP6 in a case of aneurysmal bone cyst with a complex karyotype. Rearrangement of USP6 by FISH in a similar percentage of cells (24%) compared to cells with SS18 rearrangement (25%) suggests a cryptic chromosomal rearrangement with a fusion of SS18 (18q11.2) to USP6 (17p13). This novel rearrangement probably places the coding region of USP6 under the control of SS18 promoter sequences. This case shows that rearrangement of the SS18 (SYT) locus is not conclusive evidence of synovial sarcoma, and may be present in tumors other than synovial sarcoma.
Category: Bone & Soft Tissue

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 23, Tuesday Morning


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