Improved technique for investigations on archival formalin-fixed, paraffin-embedded tumors by interphase in-situ hybridisation.

In-situ hybridisation techniques are powerful tools for the analysis of chromosomes in a variety of specimens. Due to hybridisation problems caused by extensive formalin-fixation in tissue samples mainly isolated nuclei were used for chromosomal analysis. In archival tissue, for sections to retain both an optimum of well preserved morphology and hybridisation efficiency a large-scale adjustment of protease digestion steps for each tissue block was required. We sought to develop an easy, reproducible technique by pretreatment in a 90 degrees C glycerol solution and subsequent denaturation in an autoclave 1 bar for 10 minutes. Our experiments were performed on eight up to ten years old human bladder cancer tissue blocks. Comparison with established pretreatment techniques did not reveal hybridisation differences while the morphology of tissue sections kept intact. This technique facilitates retrospective interphase cytogenetic analyses and is a reliable method for detection of chromosomal anomalies in formalin-fixed archival tumors.