## 5 Discussion
Additionally, it includes gene neighborhoods, which can be used to identify evolutionarily conserved operands in these genomes. Genome context also helps to look into phylogenetic profiles to identify genes that show similar present or absent patterns across the tree of life. The STRING database also considers curated knowledge from the manually annotated database of protein complexes and molecular pathways. Using the STRING database, we can visualize a subset of the proteins as interacting networks, and perform enrichment analysis on the entire input. KEGG pathways and GO enrichment analysis were applied to all the DEGs, and we found that they engage in a significant role in several biological processes, molecular functions, and cellular components. Moreover, we identified eight common hub genes using three methods, namely, MCC, node degree, and MNC from the Cythonuba plugin in Cytoscape. These eight hub genes are _CDK1_, _CCNA2_, _AUKRB_, _TOP2A_, _KIF11_, _ASPM_, _CENPE_, and _CCNB2_. [PERSON] et al. [48] used the MCC method to identify the hub genes that are associated with breast cancer. They found cyclin B1 (CCNB1), cyclin A2 (CCNA2), cyclin dependent kinase 1 (_CDK1_), cell division cycle 20 (_CDC20_), DNA topoisomerase II alpha (_TOP2A_), BUB1 mitotic checkpoint serine/threonine kinase (_BUB1_), aurora kinase B (_AUKRB_), cyclin B2 (_CCNB2_), kinesin family member 11 (_KIF11_), and assembly factor for spindle microtubules (_ASPM_). These genes, except for _CCNB1_, _CDC20_, and _BUB1_ are the same genes that we identified as hub genes that are associated with breast cancer. In our study, _CENPE_ is identified as one of the hub genes, but [PERSON] et al. did not identify it as one of the hub genes. _CDK1, CCNA2, AUKRB,_ and _CCNB2_ that we identified among the hub genes are also identified among the hub genes that are associated with colon cancer in a study conducted by [PERSON] et al. [49]. Moreover, in a study conducted by [PERSON] et al. [50], _CDK1, CCNA2,_ and _TOP2A_ are also identified as hub genes associated with thyroid cancer. A study for screening and identification of hub genes found that _CDK1, AUKRB, KIF11, CENPE,_ and _CCNB2_ are also associated with bladder cancer [51]. [PERSON] and [PERSON] [52] proposed overlapping modules that identify the common hub genes for five cancer types (breast, ovarian, cervical, vulvar, and endometrial). They found that _TOP2A_ and _CCNB2_ are linked to these five cancer types. We also identified these two genes among the hub genes. More recently there have been many studies designed for hub gene identification for BC. These studies include the work of [PERSON] et al. [8], and [PERSON] et al. [9]. [PERSON] et al. identified 22 DEGs from four microarray gene expression datasets (GSE65194, GSE64790, GSE41970, and GSE38959 datasets). Their analysis revealed six hub genes (TOP2A, CHEK1, CCNA2, PCNA, MSH2, and CDK6) based on the PPI network of the DEGs. They used survival analysis to assess their identified hub genes' reliability. Their results show that five of the six hub genes (TOP2A, CCNA2, PCNA, MSH2, CDK6) are associated with the triple-negative breast cancer prognosis. [PERSON] et al. identified 127 common DEGs from five microarray gene expression datasets (GSE139038, GSE62931, GSE45827, GSE42568, and GSE54002) using the LIMMA and SAM statistical methods. Thereafter, they constructed a PPI network using the string database and identified the top seven rank genes (BUB1, ASPM, TTK, CCNA2, CENPF, RFC4, and CCNB1) as hub or key genes. They then used multivariate survival analysis to validate their identified genes, and the results show that the hub genes have a strong prognosis power for BC. The hub genes identified by [PERSON] et al. and [PERSON] et al. intersect with three genes (TOP2A, CCNA2, ASPM) from the genes we identified as hub genes in our study. CCNA2 is identified as a hub gene by the studies of both [PERSON] et al. and [PERSON] et al. The contribution of this study is developing a PPI network based on an integrated analysis of RNASeq and microarray data.