Few studies have focused on antigen preservation in formalin-fixed and paraffin-embedded (FFPE) tissue in old archival material and additional studies are required, especially considering that these samples are an irreplaceable resource for scientific and clinical research. The purpose of this study is to verify antigen preservation in FFPE tissue samples stored for several decades. From the pathology archives, FFPE blocks were selected dating back to the 1960s, 1970s, 1980s, 1990s, 2000s and 2010. A panel of 12 antibodies was applied and immunoreactivities were compared. While cytoplasmic antigens showed no reduction in immunostaining intensity over time, membrane and nuclear antigens presented reduced staining intensity in older blocks. In particular, the nuclear antigen, Ki67 and CD31 showed the most pronounced antigen decay in the oldest archival blocks. In order to test possible antigen recovery, deep sectioning and lengthening of heat pretreatment were applied. Both strategies partially recover antigenicity, but their simultaneous application shows the best results.

Antigen decay in archival formalin-fixed paraffin-embedded (FFPE) tissue sections for immunohistochemistry is a well-known phenomenon which may have repercussions on translational and research studies and length of storage time appears fundamental. The aim of this study was to evaluate all possible factors which may lead to antigen decay on a prospective standardized collection of human tissues with a panel of 14 routinely used antibodies. Serial slide sections from FFPE control tissues were stored using different methods (routine storage at room temperature, Parafilm(®) protected, paraffin coated and cold stored at 4 °C) and for different time periods: 1, 6, 9, 12, 24 and 36 months. Immunohistochemistry was performed at each time cutoff simultaneously on stored sections and on freshly cut sections using a panel of 14 antibodies. Immunoreactivity was compared with immunoreactions performed at time zero. Reduction in immunostaining was observed for a subset of antibodies (CD3, CD 31, CD117, estrogen and progesterone receptors, Ki67, p53, TTF-1, vimentin) while for others (smooth muscle actin, keratins 7, 20, AE1/AE3, 34βE12), no antigen decay was observed. Loss of antigenicity was proportional to tissue section age and was dependent on mode of storage with cold storage slides being the least affected. All antigens with reductions in immunosignal were nuclear or membranous, and they all required heat pre-treatment for antigen retrieval. In contrast to results from other studies, when pre-analytical factors are strictly controlled and standardized, antigen decay seems to be restricted to nuclear or membrane antigens which require heat antigen retrieval.

To analyze expression of human leukocyte antigen-G (HLA-G) in gastric adenocarcinoma and correlate its expression with histological and clinical variables. A continuous series of 94 unselected patients with gastric adenocarcinoma (stage I to III) were selected. All histological and clinical variables were collected including the intensity of intra- and peri-tumor lymphocytic infiltration. HLA-G expression was investigated using immunohistochemistry. All histological samples analyzed for HLA-G expression were taken from the primary gastric lesion and included non-neoplastic mucosa. Evaluation of HLA-G expression was performed on the transition zone between tumor and non-neoplastic mucosa, and the invasive front of the tumor and assessment was performed as follows: percentage of positive (strong expression vs weak) cells. A variable amount of HLA-G-positive tumor cells was found in 24 out of 94 cases (25.5%). No significant correlation was found between HLA-G expression and other clinicopathological variables (sex, age, stage, grade, histotype). The overall median survival was worse in patients with HLA-G-positive adenocarcinoma (24.3 months, CI 7.7-41.0) compared to those with HLA-G-negative tumors (66.3 months, CI 53.0-79.7; p < 0.0001). Two- and 5-year survival rates of HLA-G-negative patients were 88 and 44%, respectively, while were 42 and 11% in those HLA-G-positive. This trend was observed in all stages but was more marked in stage III. HLA-G expression is associated with poor survival in stage III gastric cancer patients and represents a possible immunoescape mechanism of cancer cells.