136 Toda et al. Fig. 2. Pancytokeratin immunoreactivity toward metastatic NSCLC cells in a lymph node. The tissue sections were stained with anti- pancytokeratin antibody (AE1/AE3) using standard IHC (panel A), negative control for standard IHC (panel B), rapid AC electric field IHC (panel C), negative control for rapid AC electric field IHC (panel D), saving AC electric field IHC (dilution 1:2,000, 180 min AC electric field) (panel E), saving AC electric field IHC (panel F) procedures. Bar=100 µm. tiveness of the AC electric field on the rapid IHC procedure, we compared the abilities of the standard and rapid AC electric field IHC procedures to detect lymph node micro- metastases. Typical images of lymph node micrometastasis obtained using the rapid AC electric field IHC procedure are shown in Figure 3. Endogenous peroxidase-positive granulo- cytes were also observed around cytokeratin-positive cancer cell nests. However, the cancer cells could be distinguished from endogenous peroxidase-positive leukocytes based on their morphology. Therefore, to shorten the staining period, we did not use endogenous peroxidase blockage in the present study. Note that the lymph node micrometastases detected using the standard IHC procedure were always detectable using the rapid AC electric field IHC procedure.