Detection of Disease-specific Fusion Genes of Soft Tissue Tumors Using Formalin-fixed Paraffin-embedded Tissues; Its Diagnostic Usefulness and Factors Affecting the Detection Rates

[Background] Recent rapid advances in molecular biology have led the discovery of disease-specific novel fusion genes in a variety of soft tissue tumors. In this study, we attempted to detect these fusion genes using formalin-fixed paraffin-embedded (FFPE) tumor tissues and investigated their clinical utility and factors that affect the results of examination. [Methods] Reverse transcription polymerase chain reaction for the detection of tumor-specific fusion genes was performed using 41 FFPE tumor samples obtained from 37 patients representing nine histological types of soft tissue tumors that were diagnosed from 2006 to 2017 in our laboratory. [Results] Fusion genes in 19 (51.3%) out of 37 cases were detected successfully. Relatively high detection rates were observed in synovial sarcomas (100%, 4/4) and alveolar rhabdomyosarcomas (75%, 3/4). The detection rates of fusion genes were inversely correlated with the storage period of FFPE blocks. Decalcification by Plank-Rychlo solution significantly affected detection rates of the internal control gene (P = 0.0038). In contrast, there was no significant difference in detection rates between primary and metastatic lesion, or biopsy and resection material, or presence and absence of treatment history. [Conclusion] In certain histological types, detection of disease-specific fusion genes of soft tissue tumors using FFPE tissues showed high sensitivity and thus had diagnostic utility. However, due to the diversity of fusion patterns and the low-quality of nucleic acid, the detection rate as a whole was sluggish and required further improvement. For factors affecting the detection results, our results suggested that it was impossible to detect fusion genes by decalcified FFPE tissues, but it may be not necessary to consider factors such as the type of specimen (biopsy or resection) and treatment history of the patients when selecting the FFPE tissues.