Thanks. They cite Kim et al (1994) and Shay and Bacchetti (1997). Table 2 of Kim et al shows up to 38% telomerase activity in normal tissue (ie head and neck)

Thanks. They cite Kim et al (1994) and Shay and Bacchetti (1997). Table 2 of Kim et al shows up to 38% telomerase activity in normal tissue (ie head and neck) and in only 25% of breast cancers. Similarly Shay and Bacchetti reported telomerase activity in many normal tissue samples (eg table 2 GI tract normal was 25% table 9 normal epidermis was 44%). Also, Shay and Bacchetti write: "With very few exceptions, tumor cells were assayed by the PCR-based TRAP protocol... negative samples from the few studies that used the less sensitive assay without PCR amplification of telomerase products, have been disregarded". These papers are pretty old, so I thought it would be interesting to find out what has been learned about the TRAP protocol in the time since. Today, we know those methods lead to false positives: "The original TRAP method has several drawbacks. Initially, the CX oligonucleotide, which complementarily overlaps with TS for several bp, is used in the amplification of PCR products. It results in the dimerization of primers and products that emerge due to the interaction between primers. Even when using the optimal ACX primer with the noncomplementary TS end, a background signal may emerge during the analysis of concentrated extracts from tumor tissues [14]. An additional problem is encountered when using reverse primers which completely correspond to telomeric repeats. The primers are not annealed at the matrix edges during PCR (as a result of periodicity in telomeres), and hence false signals emerge." http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3347595/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3347595/ It would be interesting to see more recent data on this.