Using immunofluorescent digital slide technology to quantify protein expression in archival paraffin-embedded tissue sections

Molecularly targeted therapies require an adequate assessment of molecular expression in cancer. Immunofluorescent staining is a better method to quantify protein expression than immunohistochemistry (IHC), although the latter is currently used to score human epidermal growth factor receptor 2 (HER2) and steroid receptors. The quantification of signal intensity in IHC is still controversial. The advanced technology of virtual slides permits digitizing a whole slide image of immunofluorescence for a few minutes. We have established fluorescence-based, immunofluorescent quantification digital slides (IQD), a method widely applicable in routine practice. The IQD were made by scanning images of formalin-fixed, paraffin-embedded sections and contained, not only morphological information obtained from hematoxylin-counterstains, but also immunofluorescent signals. Assessing protein expression on IQD was carried out using the original image analysis software and was compared with the IHC score (HER2 and steroid receptors). There was a statistically significant correlation between the IQD and IHC scores. In addition, we compared IQD scores of groups classified by IHC scores. The IHC intermediate-expression groups were not statistically different from the high, or negative-expression groups. Immunofluorescent quantification digital slides may help pathologists to assess molecular expression in cancer tissue, and resolve the issue of scoring the intensity of brown signal on IHC slides.