Conventional HLA immunohistochemistry of formalin-fixed paraffin-embedded tissue. Using HCA2 (HLA-A heavy chain), HC10 (HLA-B/C heavy chain) and anti-B2M antibodies, loss of HLA A and B expression as detected by flow cytometry (see Figures 1 and 2) could be confirmed. In the top panel, membranous staining (arrows) of B2M, HCA2, and HC10 is observed in the moderately differentiated sigmoid adenocarcinoma of case 122. In the bottom panel, loss of HLA-A and -B is illustrated for the mucinous caecum adenocarcinoma of case 179. Tumor B2M staining was mainly restricted to the cytoplasm (arrow), but some membranous expression of B2M was observed by FCM (see Figure 1). The HCA2 and HC10 staining was completely lost in tumor epithelium (t). Typically, the retained HLA expression of stroma cells (s) resulted in an inverted staining pattern in comparison to case 122. HE, haematoxylin and eosin staining. Pictures were made at 400 × magnification, HEs at 100×.