During surgery for cancer, tissue is removed for pathologic examination to determine the nature and extent of the disease. Human tissue is normally fixed in 10% neutral buffered formalin (NBF), processed by established histologic techniques, and embedded in a paraffin wax. Cells within tissues are undergoing various phases of the cell cycle at different times. Many cells will be in the interphase portion of the cell cycle. During the interphase portion of the cell cycle, the DNA is unwound. The chromosomes are NOT distinguishable using light microscopy.
When the laboratory performs FISH in FFPE tissue, it is considered to be interphase FISH.