Loss of antigenicity with tissue age in breast cancer.

Archived tumor specimens, particularly those collected by large cooperative groups and trials, provide a wealth of material for post hoc clinical investigation. As these tissues are rigorously collected and preserved for many decades, subsequent use of the specimens to answer clinical questions must rely on the assumption that expression and detection of target biomarkers are not degraded with time. To test this assumption, we measured the expression of estrogen receptor (ER), human epidermal growth receptor 2 (HER2), and Ki67 in human breast carcinoma using quantitative immunofluorescence (QIF) in a series of formalin-fixed paraffin-embedded (FFPE) tissues from 1295 individual patients preserved for 7 to 53 years in four cohorts on tissue microarrays.