Epitope Preservation Methods for Tissue Microarrays

Objectives We sought to test recent guidelines for preserving immunoreactivity of precut slides, to quantify loss of immunoreactivity, and to determine potential for preservation by altering storage conditions. Methods Precut slides from tissue microarrays were stored under one of several conditions: exposed to ambient air at room temperature, 4°C, or -20°C or in a vacuum-sealed container at room temperature, -20°C, -80°C, or with paraffin coating. At multiple intervals over 1 year, slides were stained with antibodies against p53, isocitrate dehydrogenase 1, Ki-67, synaptophysin, and androgen receptor and evaluated. Results Compared with time 0, the overall median percentage immunoreactivity was 66% at 6 months and 51% at 1 year. During the experiment, this was as low as 55% for precut slides stored in paraffin coating and up to 87% for those stored at -20°C. Vacuum sealing was an effective preservative for some antibody targets and detrimental for others. Storage at -80°C did not have added value. Conclusions For precut slides, there is a time, storage condition, and antibody-dependent loss of immunoreactivity that could compromise analysis of prognostic, predictive, and diagnostic markers. Our findings support previous recommendations and suggest that the best storage conditions are at -20°C, without paraffin coating or vacuum sealing.