[Development of a Dual Detection Method with Fluorescence In Situ Hybridization and Immunostaining on Formalin-Fixed...

Fluorescence in situ hybridization (FISH) has recently become important for pathological diagnosis. However, its practical applications is not widespread because FISH protocol with FFPE specimens is complicated. We report a dual detection method by overlapping FISH with fluorescent immunostaining on FFPE sections. This method is characterized by changing buffers for heat treatment without proteolytic enzyme treatment. Subsequent proteolytic enzyme treatment can be omitted using an antigen activation solution, pH9 (Nichirei Corporation), for heat treatment. After the pretreatment, dual detection was achieved by DNA FISH following RNA FISH and fluorescent immunostaining. This protocol visualized gene abnormalities and protein overexpression on the same sections. Of note, in poorly differentiated tumors containing both normal and tumor cells, the tumor cells were clearly identified on the sections, and FISH signals could be counted in these cells. In addition, HER2 mRNA overexpression and gene amplification were simultaneously detected in HER2-positive gastric cancer. Thus, this method should be widely applicable in clinical settings.