Nucleic acid quality preservation by an alcohol-based fixative: comparison with frozen tumors in a routine pathology setting

Abstract

Pathologic diagnosis requires tissue fixation for histologic and immunohistologic analysis, and formalin is routinely used for this. The disadvantage of this fixative is its inability to preserve nucleic acids. Pathologic tumor diagnosis requires extensive molecular analyses, for which formalin fixation may be not adequate. Recently, an alcohol-based fixative (molecular fixative, MF) was described that allows nucleic acid preservation as well as histologic and immunohistologic studies. Moreover, the MF fixation processing system (Xpress) is fast and is well adapted to a routine process. We evaluated RNA and DNA quality within 1 month and after 1 year for 10 breast carcinomas and 20 sarcomas fixed in MF in comparison with the corresponding frozen tumors. The quality of DNA extracted from the MF-fixed tissue was similar to that extracted from the frozen tumors. The quality of RNA extracted from the MF-fixed tissue was lower than that of frozen tumors; nevertheless, a majority of RNA integrity number (RIN) values were greater than 7. Gene expression quantification by real-time polymerase chain reaction gave comparable results between tumors fixed with MF and frozen tumors. Tissue fixation at 4°C with the MF improved the RNA quality measured by the RIN value. However, after storage for 1 year at room temperature, although DNA quality was preserved, RNA extracted from tissues fixed with the MF was degraded. Tissue fixation with the MF is an important improvement for molecular pathologic diagnosis, enabling a combination of routine pathologic diagnoses and current molecular diagnoses if they are carried out near the processing time.