The age of paraffin block influences biomarker levels in archival breast cancer samples

The present study aimed to investigate the influence of paraffin block age on biomarker levels in archival breast cancer samples. Tissue blocks from five different block age groups were assessed using immunohistochemistry and fluorescence in situ hybridization. The difference in Q scores for estrogen receptor and progesterone receptor expression levels between original tests and repeated tests were significant for core needle biopsies prepared 10 years ago. The signal intensities of human epidermal growth factor receptor 2 and the centromere of chromosome 17 decreased with the age of the paraffin block. Moreover, 6 samples exhibited a negative shift in progesterone receptor Q scores for core needle biopsy samples with a Q score of 2. In conclusion, the age of paraffin blocks had significant effects on the expression levels of estrogen and progesterone receptors in core needle biopsies prepared 10 years ago. The results showed that samples with an age >7 years were not suitable for fluorescence in situ hybridization and interpretation of progesterone receptor levels for repeated core needle biopsy samples with a Q score of 2 requires caution.