BioProject

Background: As degradation of formalin-fixed paraffin-embedded (FFPE) samples limits ability to expression profile, we explored factors predicting success for FFPE profiling and investigated an approach overcoming this limitation. Methods: Bladder (n=141, stored 3-8 years) and cervix (n=160, stored 8-23 years) carcinoma FFPE samples were hybridised to Affymetrix Exon1.0ST arrays. Percent detection above background (%DABG) measured technical success. Biological signal was assessed by distinguishing cervix squamous cell carcinoma (SCC) and adenocarcinoma (AC) using a gene signature. Precursor mir-205 was measured by Exon array and mature miR-205 by qRT-PCR. Eight-old and -young cervix samples were compared using Affymetrix miRNA 2.0 arrays. For comparison, the 'cervix_tumour_cs1_113' (previsously submitted GSM677307) was included and re-analyzed with the samples from the current study (total 161 Cervix samples). Results: RNA quality controls (e.g. RNA integrity number) failed to predict profiling success, but sample age correlated with %DABG in bladder (R2=-0.30, p<0.01) and cervix (R2=-0.69, p<0.01). Biological signal was lost in older samples and neither a signature nor precursor mir-205 separated samples by histology. miR-205 qRT-PCR discriminated SCC from AC, validated by miRNA profiling (26-fold higher in SCC; p=1.10x10-5). Median miRNA probeset expression of eight-old and eight-young cervix samples correlated well (R2=0.95) overcoming the age-related bias of mRNA probesets, suggesting miR-205 stability generalises across microRNA. Conclusions: microRNA profiling overcomes the limitation of degraded FFPE samples Overall design: 48 Cervix tumour FFPE samples hybridised to exon arrays