The morbidity and mortality rates of breast cancer have risen drastically over the last few decades, and there is an urgent necessity to tailor an appropriate management and treatment strategy. A sustained decrease in breast cancer death rates could be achieved with an accurate diagnosis of cancer in the early stages. The most crucial step in achieving the best prognosis is to identify the cells that are cancerous in the early stages. Scientists have investigated numerous methods for the diagnosis of breast cancer, including mammography, positron emission tomography, magnetic resonance imaging, computed tomography, ultrasound, and biopsy. These methods are not suitable for young women and have several drawbacks, including cost and time commitment [17]. For the prediction of diseases like cancer, it becomes crucial to identify the genes that are involved in the disease development and progression. In the analysis of such genes, a Machine Learning technique like the Lasso regression method capable of handling large genetic data like the microarray sequences and adequate statistical knowledge capable of interpreting these data are required. The analysis of the microarray gene expression dataset utilized the methodology of Differential expression analysis and an efficient ML approach to find the common set of significant genes. The DEG analysis compares the degree of expression in the diseased and control groups using a variety of statistical techniques, including the t-test of cohorts. On the other hand, the LASSO-regression classifies the data using its statistical machine-learning approach. While this approach works well, it is limited by the presence of a large amount of noise in the gene expression data, the repeatability of the results, and individual differences due to age, gender, genotype, stage of illness, and other variables. This disadvantage can be removed by implementing a statistical meta-analysis of combined different studies which would enable us to find the distinct disease signatures that are typically consistent in several studies. [18]. Another drawback of using the LASSO-based classifier is that it requires a large set of data for initial training purposes. The dataset should also be balanced which means there should not be any large difference between the counts of the two categories. The LASSO-based classifier implemented in this study demonstrated a significant classification accuracy of 96.6%. From the DEGs identification through “limma” we got a total of 5879 differentially expressed genes. The intersection of these two sets obtained from LASSO and LIMMA gave 230 genes of interest which were used in further analysis. The genes of interest were subjected to Reactome and GO pathway analysis through Enrichr. The genes were enriched in significant GO terms like Cytokine Activity (GO:0005125), Chemokine Activity (GO:0008009), Chemokine Receptor Binding (GO:0042379), Positive Regulation Of MAPK Cascade (GO:0043410), Neutrophil Chemotaxis (GO:0030593). Earlier studies have shown that Cytokines actively take part in processes involved in tumor onset, promotion, angiogenesis, and metastasis in breast cancer [19]. Angiogenesis creates blood vessels that give the necessary nutrients and oxygen for tumor development in solid malignancies. This mechanism appears to be a well-defined characteristic of cancer and has been shown in several studies to play a critical role in the origin of cancer metastasis. This process is highly controlled, most notably by angiogenesis-promoting or angiogenesis-inhibiting cytokines [20]. Breast cancer is largely caused by persistent inflammation, which is the initial step of malignant growth [21]. Research has indicated that persistent inflammation could increase the probability of developing breast cancer. Additionally, inflammatory regulatory factors secreted by breast cancer cells might facilitate the advancement of inflammation, so establishing a vicious cycle whereby inflammatory tumors enhance the evolution of cancer [22]. These inflammations could trigger inflammatory mediators which result in the production of nonspecific proinflammatory cytokines (TNF-α [tumor necrosis factor-α], IL-6, and IFN-α), which can then trigger the development of chemokines to further inflammation [23]. Studies have shown that in the inflammatory microenvironment, the chemokines and chemokine receptors can support tumor development. According to clinical research, there is a strong correlation between the development of tumours and the overexpression of certain chemokines in breast cancer [25]. Central signaling pathways known as MAPK cascades control a broad range of stimulated cellular processes, such as stress response, apoptosis, differentiation, and proliferation. Consequently, dysregulation, or improper functioning of these cascades, plays a role in the onset and development of illnesses like diabetes, cancer, autoimmune disorders, and faulty developmental processes [26]. Human tissues contain three main MAP kinase pathways; however, the one that involves ERK-1 and − 2 is more pertinent to breast cancer. The primary regulators of ERK-1 and − 2 are peptide growth factors that function through receptors that include tyrosine kinase. A variety of additional ligands can also function non-genomically by activating MAP kinase through heterotrimeric G protein receptors, including progesterone, testosterone, and estradiol. According to recent research, there is often a higher percentage of cells with active MAP kinase in breast tumors [27]. The most prevalent leukocytes in the body, neutrophils, are becoming more well-acknowledged for their potential to actively modulate cancer. In the bloodstream, neutrophils escort circulating tumor cells to promote their survival and stimulate their proliferation and metastasis. Tumor-infiltrating neutrophils (TINs) are the neutrophils that are found in the tumor microenvironment (TME) and interact with cancer cells [28]. High TIN levels have been linked to advanced histologic grade, tumor stage, and the TNBC subtype [29].
In the REACTOME Pathways, some of the significant terms were: GPCR Ligand Binding (R-HSA-500792), Signaling by GPCR (R-HSA-372790), Chemokine Receptors Bind Chemokines (R-HSA-380108). The biggest family of cell-surface receptors, the G protein-coupled receptors (GPCRs), play a role in the initiation and progression of several malignancies, including breast cancer. Due to their abnormal activation and overexpression, GPCRs are commonly linked to several features of cancer, such as angiogenesis, metastasis, tumour development, invasion, migration, and survival [30]. The chemokine activities also come under significance in the pathway analysis, brief discussion on their activities has been previously discussed.
This study found 6 prognostic signature genes namely CCL24, CCL21, CCR8, CXCL11, CCL28 and CCL23 which all belong to the chemokine family. The relative expression profiles are shown in Fig. 7. CCR8 which is a cell surface receptor that belongs to Class A of the G protein-coupled receptor (GPCR) family is observed to be upregulated in breast cancer patients. Studies show that it is well CCR8 is essential for recruiting Tregs to the tumor site and creating an immunosuppressive environment that facilitates tumor escape. This recruiting mechanism can be interfered with by inhibiting CCR8, which may enhance anti-tumor immune responses and slow tumor development [31]. According to current studies, anti-CCR8 antibodies can impair CCR8 activity, which lowers the number of Treg cells accumulating in tumors and interferes with their immunosuppressive role [32]. The KM plot analysis [Figure 8] though shows conflicting results. The Overall Survival (OS) analysis shows that under expression of CCR8 decreases OS. This could be partially attributed to the fact that at the initial stages of the tumor development, the cytokines could show anti-tumour activity [33]. Further studies in this regard are required. CXCL11 is a chemokine superfamily member of the CXC family and has been found to play a significant role in the development of breast cancer [34]. This molecule has been suggested to be the major ligand for CXCR3 and encodes the protein that activated T-cells need to trigger the chemotactic response. Research shows that CXCL11 activates ERK, which in turn promotes the migratory, invasive, and proliferative activities of MDA-MB-231 cells [35]. It is also exhibited by the KM plot that overexpression of CXCL11 decreases OS. From the analysis of the expression profiles [Figure 7], it is evident that the transcription levels of CCL 21/24/23/28 in breast cancer samples were decreased significantly [36]. This study similar to the previous ones proves that low expression of CCL21 is associated with worst OS. CCL21 is linked to enhanced immunogenicity in breast cancer. CCL24 which exhibits a high expression level in several types of cancer, this study found that it is under-expressed in breast cancer with no significant relation with OS. Again, previous works have shown that a reduction in the chemokine CCL23 in hepatic tumors is linked to a poor prognosis for HCC patients and may be a strategy used by the tumor cells to avoid the immune system [37]. The current study also confirms these results evident from the expression profile and Survival analysis. Studies have exhibited Oral squamous cell carcinoma cells with detectable RUNX3 expression levels, CCL28 prevented invasion and the epithelial-mesenchymal transition (EMT). Its suppression of EMT was characterized by enhanced E-cadherin expression and reduced nuclear localization of β-catenin. RARβ expression was elevated by CCL28 signaling through CCR10, which also decreased the interaction between RARα and HDAC1 [38]. In the present study, it has been observed that CCL28 is under expressed, confirming previous studies [39]. Studies have demonstrated the involvement of CCL28 and CCL27 in the immune system's anticancer response. These chemokines cause anticancer NK cells to infiltrate the tumor, improving the prognosis through a higher expression of these chemokines in the tumor [40]. The results highly support the fact that the chemokines that modulate immune cell trafficking play a crucial role in breast cancer tumor microenvironment perturbations. They play a significant role in immune cell infiltration in the tumor progression and could show anti-cancer properties, as well as some pro-cancer characteristics and thus they play an important role in neoplasia.