Molecular pathology of paraffin-embedded tissue. Current clinical applications.

Molecular biology techniques have been adapted to analyze paraffin-embedded tissues, expanding their potential clinical utility. The isolation of intact nucleic acids from tissue blocks is fundamental to the molecular pathology of paraffin-embedded tissues. In vitro amplification with the polymerase chain reaction (PCR) promises to be the most useful means of retrospective analysis since it can be performed successfully on DNA that has partially degraded during fixation, paraffin embedding, and the extraction process. Four clinical situations in which DNA analysis of paraffin-embedded tissues can be helpful are: (a) gene rearrangement analysis in lymphoproliferative disorders, where fresh tissue has not been obtained at the time of surgery; (b) identification of infectious agents, particularly viruses; (c) genetic testing of families with a putative inherited disease where the affected member has died; and (d) specimen identification. The PCR and other techniques of genetic analysis are powerful in sensitivity and specificity when performed and interpreted with appropriate precautions and controls. DNA analysis of paraffin-embedded tissues will likely become a fixed part of the future pathologist's diagnostic armamentarium.