Background: Cognitive problems have been reported in breast cancer patients after chemotherapy. A small group of older breast cancer survivors carrying the APOE4 gene, receiving chemotherapy, was at increased risk of long-term impairment of brain function. We have analyzed the expression of APOE and the next 23-ranked Alzheimer's disease (AD) susceptibility genes in malignant breast tumors. We wished to determine if these 24 genes might be related to breast cancer.
Methods: To identify the most important AD susceptibility genes, we consulted the ALZGENE database (www.alzgene.org/) which displays this information and regularly updates it. To analyze the effect of AD susceptibility genes on breast cancer, we used The Cancer Genome Atlas (TCGA). We analyzed TCGA data with cBioPortal for Cancer Genomics. cBioPortal provides visualization, analysis, and download of large-scale cancer genomic data sets. cBioPortal can analyze APOE in breast tumors but cannot distinguish its three alleles: E2, E3, and E4.
Results: About 1.6% of the tumors had APOE amplification (copy number alteration). Two percent of the tumors had CD33 alterations. None of the tumors had APOE mutations. Two tumors had CD33 missense mutations of unknown significance. Expression heatmap shows that over- or underexpression of APOE and CD33 was correlated in most of the tumors. APOE alteration significantly co-occurred with CD33 and CD2AP.
Conclusion: Alterations of certain cancer genes tend to co-occur, indicating that they may work in tandem to drive tumor formation and development. This may be the case with the co-occurring alterations of APOE, CD33, and CD2AP. It would be important to know which APOE allele(s) were co-occurrent with CD33 and CD2AP and whether co-occurrence in the tumor predicted increased risk of AD. This information could help in identification of specific risk factors for breast cancer-related cognitive decline in older women, which has important implications for oncology care.
Keywords: The Cancer Genome Atlas; cBioPortal; co-occurrence; dementia.