BioProject

Background: Interval breast cancers can occur through failure to detect an abnormality at the time of screening (missed interval cancer), or as a new event after a negative screen (true interval cancer). The development and progression of true interval tumors (TIBC) is known to be different than screen-detected tumors (SDBC). However, much work still needs to be done to understand the biological characteristics and clinical behaviour of these TIBC. Objectives: To characterize the gene expression profile in TIBC and SDBC aimed to identify biological markers that may be associated with the emergence of symptomatic breast cancer in the screening interval. Material and Methods: An unsupervised exploratory gene expression profile analysis was performed among 10 samples (discovery set, TIBC=5 and SDBC=5) using Affymetrix Human Gene 1.0 ST arrays and interpreted by Ingenuity Pathway Analysis. Differential expression of selected genes was confirmed in validation series of 91 patients (TIBC=12 and SDBC=79) by immunohistochemistry and 24 patients (TIBC=8 and SDBC=16) by RT-qPCR, expanding the analysis to other genes in same pathway (mTOR, 4E-BP1, eIF-4G and S6). Results: Exploratory gene expression analysis identified 1060 transcripts with a p value <0.05 and 132 transcripts with an adjusted p value <0.01 difference between TIBC and SDBC samples. Based on biological implications in breast cancer, four genes were selected for further validation: CP (ceruloplasmin) and RPS6KB2 (ribosomal protein S6 kinase, 70kDa, polypeptide 2) both up-regulated in TIBC vs SDBC and PTEN (phosphatase and tensin homolog) and TGFBR3 (transforming growth factor beta receptor III), down-regulated in TIBC vs SDBC. Their differential expression was confirmed by RT-qPCR and immunohistochemistry, suggesting mTOR pathway overexpression in TIBC at both mRNA and protein level. Further expanded analysis by immunohistochemistry for mTOR pathway activation, including expression of phosphorylated forms of mTOR, 4E-BP1, eIF-4G, RPS6KB2 and S6, confirmed the upregulation of this pathway in TIBC. Conclusions: TIBC and SDBC shows differential expression profile both at the gene and protein levels. The mTOR signaling is significantly upregulated in TIBC compared with SDBC, suggesting an enhanced aggressiveness of TIBC. Besides, CP may also represent novel immunohistochemical marker helpful in distinguishing between TIBC and SDBC. Further studies with larger sets of patients are guaranteed to verify these findings associated with TIBC. Overall design: 5 TIBC samples where compared with 5 SDBC