The diagnosis of small round cell
sarcomas is often very difficult, especially when only small biopsy specimens are available for examination. Recent studies have shown that some
sarcomas have specific recurrent
chromosomal translocations producing chimeric gene fusions, which can be detected by reverse transcription-polymerase chain reaction (RT-PCR), fluorescent in situ hybridization (FISH), or cytogenetic analysis. In this study, 12 cases of well-defined
sarcomas including
Ewings sarcoma/
primitive neuroectodermal tumors (ES/
PNET),
synovial sarcoma (SS),
alveolar rhabdomyosarcoma (ARMS), and desmoplastic small round cell
tumors (DSRCT) were used to collect specific numbers of cells by
laser capture microdissection (LCM), subsequently used for RT-PCR to detect specific chimeric gene transcripts.
Tumor cells from fresh-frozen (FS) tissue sections and
paraffin-embedded (PS) tissue sections from the same cases were compared directly to evaluate the sensitivity of FS and PS sections as the starting material for analysis. Samples were used for
RNA extraction, RT-PCR analysis, and Southern hybridization with
fluorescein-labeled internal probes followed by enhance chemiluminescence (ECL) detection. The fusion gene transcripts could be detected using 50 cells from FS materials in all cases and from 1 cell in 9 of 12 cases. For PS, a positive signal could be detected using 200 to 1000 cells in all cases, while weaker signals were detected using 50 cells in most cases. These results indicate that the fusion gene products from small round cell
sarcomas can be detected by RT-PCR with 10 to 200 cells from FS and PS tissues. The sensitivity of RT-PCR with FS was 10- to 50-fold greater than with PS. These results also suggest that RT-PCR analysis for
sarcoma fusion gene products can be successfully performed when only a few cells are available for analysis, although this is not recommended for routine clinical use.