[60] TFE3 Gene Rearrangement Status Is Heterogeneous in Alveolar Soft Part Sarcomas: A Study by Dual-Color Chromogenic In Situ Hybridization on Formalin-Fixed Paraffin-Embedded Samples

Toru Motoi, Akihiko Yoshida, Ikuma Kato, Tsunekazu Hishima, Kaori Tsuji, Tetsuo Imamura, Toshio Fukusato. Tokyo Metropolitan Cancer and Infectious Disease Center Komagome Hospital, Tokyo, Japan; The University of Tokyo, Tokyo, Japan; Teikyo University Hospital, Tokyo, Japan; Teikyo University, Tokyo, Japan

Background: Alveolar Soft Part Sarcoma (ASPS) is a rare soft tissue sarcoma of unknown histogenesis. Cytogenetically, ASPS invariably shows a specific unbalanced translocation involving the chromosomes X and 17, which results in ASPL-TFE3 fusion gene. Using dual-color chromogenic in situ hybridization (dc-CISH) that enables simultaneous morphologic and cytogenetic assessment at cellular level under bright-field microscope, we examined cell-type-specific TFE3 gene status on formalin-fixed paraffin-embedded samples (FFPEs).
Design: We retrieved 5 ASPS cases. Prior to dc-CISH, they were confirmed by RT-PCR to harbor ASPL-TFE3 fusion. The FFPEs of these were studied by dc-CISH using custom-made break-apart probes for TFE3, visualized by DAKO duoCISH. The TFE3 gene status of neoplastic and non-neoplastic cells was separately evaluated by examining 100 cells each. The dc-CISH signal pattern of typical unbalanced translocation shows an additional isolated 3′ signal. TFE3 protein expression was also evaluated immunohistochemically by assessing 1000 cells of each cell type.
Results: ASPS tumor cells showed heterogeneous signal pattern by dc-CISH in all samples. The cells with typical unbalanced translocation pattern ranged from 1 to 19% (mean 13%) of tumor cellularity, while the cells with split 3'- and 5'- signals and thoese with no translocation patterns constituted 8−70% (mean 28%) and 16−65% (mean 36%), respectively. TFE3 rearrangement was absent in non-neoplastic cells. Immunohistochemically, diffuse and strong nuclear TFE3 staining was observed in 86.3−96.5% (mean 92.7%) of tumor cells, whereas non-neoplastic cells showed no immunoreactivity.
Conclusions: The TFE3 gene status was found quite heterogeneous in ASPS and only a subset of tumor cells showed the signal pattern of typical unbalanced translocation. This intratumoral genetic heterogeneity has never been documented by conventional RT-PCR and FISH, and is in contrast to what one would expect for typical translocation-associated sarcomas. Thus, care should be taken when diagnosing ASPS by CISH or FISH. Despite cytogenetic heterogeneity, TFE3 protein expression was diffuse and homogeneous. Such discordance may indicate rearrangement-independent expression mechanisms, and examples may include complex epigenetic regulation.
Category: Bone & Soft Tissue

Monday, March 19, 2012 1:00 PM

Poster Session II # 14, Monday Afternoon

 

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