[74] Advantage of FISH Analysis Using PDGFB Dual-Color, Break-Apart Probes for an Adjunct to Diagnosis of Dermatofibrosarcoma Protuberans
T Mitsuhashi, H Asanuma, T Matsumura, N Tochigi, T Shimoda, T Hasegawa. Sapporo Medical University, Sapporo, Japan; National Cancer Center Hospital and Research Institute, Tokyo, Japan
Background: Dermatofibrosarcoma protuberans (DFSP) represents a low-grade mesenchymal neoplasm of fibroblast/myofibroblast, and it occasionally contains fibrosarcoma (FS) component. Cytogenetically, all forms of DFSP are characterized by t(17;22)(q22;p13) translocation, with some cases resulting in supernumerary ring chromosomes. This translocation fuses the collagen type I 
1 (COL1A1) gene to the platelet-derived growth factor 
-chain (PDGFB) gene. While many CAL1A1 gene breakpoints have been identified, PDGFB gene breakpoint is remarkably constant. In this study, we investigate the advantage of fluorescence in-situ hybridization (FISH) using newly developed dual-color, break-apart (NDDCBA) probes for PDGFB at diagnostic laboratories for the application to pathological diagnosis and therapeutic interventions.
Design: Formalin-fixed paraffin-embedded (FFPE) tissues from 13 DFSP (including FS in 3 cases) and 13 control superficial spindle cell tumors were used. The expression of CD34 and PDGFB receptor (PBGFRB) were evaluated immunohistochemically, and FISH analysis was performed using NDDCBA probes for PDGFB. In FISH analysis, only distinct split signals were counted in 50 tumor cells, and the results were regarded as positive if more than 10% of tumor cells show split signals, green (G) and orange (O). In addition, it was regarded as amplification if extra signals were observed, and amplification rate was calculated by 50 tumor cells.
Results: Immunohistochemically, all DFSP were CD34+, and all DFSP and FS component were PDGFRB+, either diffusely or focally. In FISH analysis for PDGFB, signals were detected in 9 of 13 cases of DFSP (with or without FS), and in 11 of 13 cases of control.
| Split signals (%) | G/O ratio (mean) | Amplification rate in % (mean) | |
| DFSP (n=9) | 9/9 (100) | 1.47-3.3 (2.22) | 70-90 (80) |
| FS (n=3) | 3/3 (100) | 1.51-2.0 (1.70) | 72-94 (82) |
| Control (n=11) | 0/0 (0) | 0.95-1.02 (0.99) | 0-14 (7.6) |
Conclusions: FISH analysis using NDDCBA probes for PDGFB was enabled by FFPE DFSP tissues. Its detection is particularly helpful in the differential diagnosis of atypical, fibrosarcomatous, and metastatic DFSP, and may be useful to evaluate the application of imatinib to non-resectable, recurrent and metastatic DFSPs.
Category: Bone & Soft Tissue
Monday, March 9, 2009 1:00 PM
Poster Session II # 15, Monday Afternoon