Fibroblast activating protein-α expression in squamous cell carcinoma of the esophagus in primary and irradiated tumors: the use of archival FFPE material for molecular techniques

There are numerous reports suggesting that fibroblast activating protein-α (FAP-α) plays an important role in invasion of various tumor types. We studied the expression pattern of FAP-α in esophageal squamous cell carcinoma (ESCC) patients who had not been treated primarily and those who had received neoadjuvant radiochemotherapy. Our goal was to establish whether readily available tissue specimens fixed in formalin and stored in paraffin blocks for years might still be a source of FAP-α RNA for PCR analysis. The study included 20 patients divided into two groups, 10 patients in each group. We evaluated the expression of FAP- α by PCR techniques in fresh frozen and in paraffin-embedded tissues, and compared it to the expression in non-cancer tissues. To detect the protein expression level of FAP-α in paraffin-embedded tissues we used chromogenic immunohistochemical (IHC) staining. Data were analyzed by t-test or the nonparametric Wilcoxon matched pair test using Statistica 12.5 software. We observed an increased level of the FAP-α gene and protein expression in cancer tissues when compared with their corresponding normal tissues. However, statistically significant differences were found only in the group of patients untreated before surgery. RNA extracted from paraffin-embedded tissue sections had very low quality, especially in the context of degradation. FAP-α remains a highly altered participant of a complex microenvironment in esophageal squamous cell carcinoma, and its role in cell signaling requires further study. In this paper, we conclude that the use of a regular RT-PCR method for diagnostic purposes, which we have presented in an earlier paper, can be as good as qRT-PCR. Also, immunohistochemistry proved to be very useful and the only reliable method that can be used on longterm stored formalin-fixed, paraffin-embedded tissues.