Parametric mapping of immunohistochemically stained tissue sections; a method to quantify the colocalization of tumor markers

Background Automated analysis of immunohistochemically stained tissue sections is of great importance in cancer research to detect tumor-specific prognostic markers and make therapy decisions. Here, an automated quantitative analysis is presented to assess the colocalization of CAIX, a membrane-bound hypoxic marker and Ki-67, a nuclear proliferation marker. Methods Tissue sections of 104 biopsies from 89 patients were stained for CAIX and Ki-67 with diaminobenzidine and haematoxylin counterstain. Image scans of whole tumor sections were recorded and image maps were created with parametric mapping to quantify the markers and assess the colocalization. Results The fraction of CAIX showed a range of 0-93%. The interobserver correlation and the correlation between manual scores and automated analysis were both very strong (rs=0.96, p <0.0001, and rs=0.97, p <0.0001). The labelling index of Ki-67 exhibited a range of 0-42% with less strong interobserver and manual to automated analysis The relative tumor area positive for both markers varied from 0 - 76%. Conclusion Parametric mapping of immunohistochemically stained tumor sections is a reliable method to quantitatively analyze membrane-bound proteins and assess the colocalization of various tumor markers in different subcellular compartments.