Gene expression profiling in true interval breast cancer reveals overactivation of the mTOR signaling pathway

The development and progression of true interval breast cancers (tumors that truly appear after a negative screening mammogram) is known to be different from screen-detected cancers. However, the worse clinical behavior of true interval cancers is not fully understood from a biologic basis. We described the differential patterns of gene expression through microarray analysis in true interval and screen-detected cancers.

True interval and screen-detected cancers show differential expression profile both at gene and protein levels. The mTOR signaling is significantly upregulated in true interval cancers, suggesting this pathway may mediate their aggressiveness. Impact: Linking epidemiologic factors and mTOR activation may be the basis for future personalized screening strategies in women at risk of true interval cancers.

An unsupervised exploratory gene expression profile analysis was performed on 10 samples (true interval cancers = 5; screen-detected cancers = 5) using Affymetrix Human Gene 1.0ST arrays and interpreted by Ingenuity Pathway Analysis. Differential expression of selected genes was confirmed in a validation series of 91 tumors (n = 12; n = 79) by immunohistochemistry and in 24 tumors (n = 8; n = 16) by reverse transcription quantitative PCR (RT-qPCR), in true interval and screen-detected cancers, respectively.

Exploratory gene expression analysis identified 1,060 differentially expressed genes (unadjusted P < 0.05) between study groups. On the basis of biologic implications, four genes were further validated: ceruloplasmin (CP) and ribosomal protein S6 kinase, 70 kDa, polypeptide 2 (RPS6KB2), both upregulated in true interval cancers; and phosphatase and tensin homolog (PTEN) and transforming growth factor beta receptor III (TGFBR3), downregulated in true interval cancers. Their differential expression was confirmed by RT-qPCR and immunohistochemistry, consistent with mTOR pathway overexpression in true interval cancers. Conclusions: True interval and screen-detected cancers show differential expression profile both at gene and protein levels. The mTOR signaling is significantly upregulated in true interval cancers, suggesting this pathway may mediate their aggressiveness. Impact: Linking epidemiologic factors and mTOR activation may be the basis for future personalized screening strategies in women at risk of true interval cancers.