The increasing incidence and mortality rates of endometrial cancer highlight the critical need for new molecular biomarkers [30,31,32]. These biomarkers are essential for early diagnosis, accurate prognosis, and the development of effective treatment strategies. Advances in molecular classification, particularly in identifying distinct subtypes, are revolutionizing the approach to endometrial cancer care. This progress, combined with emerging blood-based biomarkers, significantly enhances early detection, enables more precise prognostic assessments, and supports the implementation of targeted therapies [33,34,35,36]. Broadening the search for and application of these molecular markers is pivotal in advancing personalized medicine, leading to more customized and efficacious treatments, ultimately improving outcomes and the quality of life for patients with endometrial cancer.

Recent analyses have confirmed CPA4 as a potential biomarker for early cancer diagnosis. In bladder cancer, CPA4 overexpression correlates with poor survival outcomes, similar to findings in endometrial cancer. The link between CPA4 expression and immune cell infiltration in tumors, as evidenced in bladder cancer, may also extend to endometrial cancer, considering the immune system's role in cancer development and progression [18].

The Human Protein Atlas indicates that CPA4 is an oncogene that is enhanced in certain cancers, with its expression significantly correlated with various malignant tumor characteristics, such as size, staging, lymph node metastasis, depth of invasion, and distant metastasis [14, 16, 17]. Studies have demonstrated that high expression of CPA4 is significantly associated with the TNM staging, lymph node metastasis, and distant metastasis of pancreatic cancer [13]. In gastric cancer research, CPA4 expression has been found to be positively correlated with Ki67, a proliferation marker, and negatively correlated with p53, a tumor suppressor protein, suggesting that CPA4 may exert its effects by influencing these key factors in tumor progression. CPA4 expression in bladder cancer [18] has also been linked to the infiltration of various immune cells, including Th1 cells, Th2 cells, T-cell exhaustion, and tumor-associated macrophages (TAMs), indicating that CPA4 may play a role by affecting the infiltration of immune cells in the tumor microenvironment.

Studies in other cancer types, such as breast cancer, have found serum and mRNA levels of CPA4 to be associated with disease aggressiveness and progression, highlighting its potential as a diagnostic and prognostic marker [19]. The expression of CPA4 in the endometrium has been documented, with specific data on its RNA expression levels and cell-type specificity, which may inform its expression patterns in endometrial cancer. The observed correlation between CPA4 expression and Ki67, a marker of proliferation, could suggest a role in tumor growth and histological grading, which may be explored further in endometrial cancer.

Given the complexity of cancer biology, these findings should be contextualized within the larger framework of tumor microenvironment interactions and genetic variability among patients. The integration of CPA4 expression data with clinical outcomes and molecular profiling in endometrial cancer could provide insights into its potential as a therapeutic target or a component of prognostic models.

To strengthen the discussion, further research could focus on the functional role of CPA4 in endometrial cancer, exploring how its expression affects tumor behavior and response to therapy, and how it might interact with known pathways of endometrial carcinogenesis.

To elucidate the role of CPA4 in tumorigenesis and its association with the 16 hub genes identified in single-gene differential analysis and correlation analysis, an integrative approach is warranted. These hub genes include S100A7, IVL, members of the SPRR family, CASP14, RPTN, CDSN, PI3, and LOR. The comprehensive analysis of literature indicates a multifaceted role of CPA4 in cancer, particularly through its association with hub genes involved in keratinocyte differentiation and function. The exploration of these hub genes and their relationship to cancer can provide insights into the potential functions of CPA4 in endometrial cancer.

S100A7, also known as psoriasin, is associated with tumor progression and has been suggested as a potential diagnostic and prognostic biomarker for esophageal cancer [37, 38]. Its role in promoting migration, invasion, and metastasis of human cancer cells highlights its involvement in aggressive cancer behavior [38]. Moreover, it has been implicated in breast cancer progression, indicating its relevance across different types of cancers [39, 40].

The IVL gene, which codes for involucrin, a protein involved in the formation of the cell envelope in keratinocytes, shows a pattern of downregulation in oral malignancies and is associated with poor differentiation and reduced overall survival [41]. This loss of expression might be indicative of a compromised epithelial barrier, which could be relevant to the progression of endometrial cancer.

The SPRR family genes are associated with increased epithelial proliferation and malignant processes [42]. Specifically, SPRR1B has been identified as a significant prognostic gene in lung adenocarcinoma, indicating its role in cancer prognosis [43]. The involvement of these genes in colorectal tumors and their upregulation in lung squamous carcinoma further underscore their importance in tumorigenesis [44, 45].

CASP14, a member of the caspase family, is notably higher in triple-negative breast cancer (TNBC) tissues compared to other subtypes, linking it to cancer aggressiveness [46]. It has been implicated in brain metastatic breast cancer and is associated with cancer progression in ovarian and colon cancer [47, 48].

The collective findings from these genes suggest that CPA4, through its interaction with them, may be involved in cell differentiation, immune regulation, and the epithelial-to-mesenchymal transition, all of which are pivotal in cancer progression. Therefore, by understanding the functions of these hub genes, we can predict the potential role of CPA4 in endometrial cancer, particularly in its capacity to affect cell proliferation, differentiation, and possibly immune evasion.

The above synthesis indicates that CPA4, in conjunction with its associated hub genes, may be a key player in the complex molecular pathways that contribute to the development and progression of endometrial cancer. It could potentially serve as a biomarker for cancer aggressiveness and a target for therapeutic intervention. Future research should focus on elucidating the precise molecular mechanisms by which CPA4 and these hub genes contribute to endometrial carcinogenesis and on verifying these findings in clinical settings.

Through a differential expression analysis focused on CPA4, we identified 41 genes associated with CPA4 expression, including KRT16, KRT17, and KRT80, which belong to the keratin family. The high expression of these keratin genes in endometrial cancer tissues may be linked to phenotypic changes in cancer cells and an increase in tumor invasiveness. Alterations in keratin expression can potentially affect the stability of the cytoskeleton and cell–matrix interactions, thereby promoting cancer cell migration and metastasis.

MMP1, a matrix metalloproteinase, is well-known for its critical role in tumor invasion and metastasis [49]. Reduced expression of MMP1 may indicate a decreased requirement for extracellular matrix degradation by tumor cells [50], which could, in turn, limit their invasive capabilities. Conversely, the downregulation of NDRG1 [51]might be associated with cellular stress responses and changes in the tumor microenvironment. IL36RN, an immune-related gene, is highly expressed and may reflect immune dysregulation within the tumor microenvironment, further influencing cancer progression [52]. PADI1 and PADI3 are involved in post-translational protein modification, and their aberrant expression could impact the biological behavior of cancer cells [53]. In addition, LZTS1 and TRIM29 may contribute to the development of endometrial cancer by regulating cell cycle and apoptosis [54].

It can be speculated that the changes in CPA4 expression may influence the occurrence and development of endometrial cancer by regulating the expression of the aforementioned genes. These gene alterations may lead to the remodeling of the tumor microenvironment, enhancing the survival capability of tumor cells and promoting tumor progression. In addition, the immune-related characteristics of these genes may also suggest a possible association between CPA4 and tumor immune evasion. Therefore, in-depth research on the specific mechanisms of action of these genes and CPA4 in endometrial cancer could potentially provide new therapeutic targets for this disease.

The functional enrichment analyses of CPA4 and its differentially expressed genes in the context of endometrial cancer progression have brought to light the significance of several biological processes and molecular functions. The keratinization process, which involves the production of the protective protein keratin, though generally a protective mechanism for the skin, can abnormally contribute to the development of cancers, such as squamous cell carcinoma. This aberrant keratinization indicates a potential role for CPA4 in epithelial tumorigenesis, given keratins' active involvement in cancer cell invasion, metastasis, and treatment responsiveness [55].

Further examination reveals that CPA4-associated genes are actively involved in G-protein coupled receptor (GPCR) binding, an integral part of cellular signaling that governs tumorigenesis including proliferation, invasion, and survival [56,57,58]. The dysregulation of GPCRs is a common feature in various cancers, implicating CPA4 in the modulation of these receptors, possibly influencing cancer stem cell maintenance and progression [59].

The estrogen signaling pathway’s enrichment suggests that CPA4 may also play a role in hormone-dependent cellular processes. Estrogens are known to modify the DNA damage response and DNA repair mechanisms, leading to cancer progression and chemoresistance [60,61,62]. Given the prominence of estrogen signaling in endometrial cancer, CPA4 could influence disease progression by interacting with this pathway [63].

Complement and coagulation cascades, part of the innate immune response, are also implicated in cancer progression, with these pathways potentially correlating with chemosensitivity and patient survival [64]. The involvement of CPA4 in these cascades indicates a potential impact on the inflammatory response and tumor microenvironment, which are crucial for cancer development and metastasis [65, 66].

Moreover, the KRAS signaling pathway, which is central to cell growth, differentiation, and survival, is often dysregulated in cancer due to mutations [67, 68]. CPA4's association with this pathway suggests it may influence the tumorigenesis process, particularly since KRAS mutations lead to uncontrolled cell proliferation and are present in a significant fraction of cancers [69, 70].

Finally, the epithelial-to-mesenchymal transition (EMT) process, which is facilitated by CPA4-related pathways, is critical in cancer progression as it enables tumor cells to disseminate, invade, and form metastases [71, 72]. The association with EMT also highlights CPA4's possible contribution to the aggressive behavior of endometrial cancer cells, including their chemoresistance and poor prognosis.

In summary, CPA4 is poised at the intersection of multiple signaling pathways that are critical for the progression of endometrial cancer. These include the regulation of epithelial cell function, immune system interactions, hormonal responses, and the cell's invasive and metastatic capabilities. As a result, CPA4 emerges as a potential biomarker for cancer aggressiveness and a promising target for therapeutic intervention. Future research should focus on elucidating CPA4's molecular mechanisms within these pathways to provide new insights into endometrial cancer's molecular underpinnings and pave the way for novel therapeutic strategies.

Utilizing multivariate Cox regression results, a predictive tool in the form of a nomogram plot was constructed to analyze the model's accuracy. The survival prediction plots for 1, 3, and 5 years showed a good correlation with actual values, suggesting that this model may emerge as a novel and valuable method for prognosis estimation. The Cox regression analysis of clinical samples and the validation of the prognostic nomogram model further support the prognostic value of CPA4 in endometrial cancer. Although other variables, such as FIGO stage and Ki67 index, also demonstrated significant prognostic relevance, the expression level of CPA4 remained an independent prognostic marker. This finding strengthens the hypothesis that CPA4 could be a potential therapeutic target in endometrial cancer. Previous extensive research on molecular biomarkers for endometrial cancer has proposed the use of both protein-coding RNAs and non-coding RNAs as predictors for the incidence and prognosis of the disease [73, 74]. Studies have indicated that genes such as PTEN, KNL1, PPP2R1A, PPP1R14B, L1CAM, and CTNNB1 are associated with the occurrence, progression, and prognosis of UCEC [75]. These findings support the feasibility of CPA4 as a potential molecular marker to aid in the diagnosis and prognostic assessment of endometrial cancer.

Furthermore, although specific inhibitors targeting CPA4 are still in the early stages of research, several studies have laid a critical foundation for their development. Kayashima et al. were the first to reveal the imprinted gene characteristics of CPA4 [10], while Pallarès et al. and Covaleda et al. further elucidated the interactions between CPA4 and its endogenous inhibitors [70, 71]. These studies provide the structural basis for future efforts in screening and designing CPA4 inhibitors. In addition, research by Kim et al. demonstrated that natural products or plant extracts, such as CPA4-1, exhibit inhibitory effects in animal models, offering a new direction for future therapeutic research [72]. Future studies should focus on screening more effective CPA4-specific inhibitors and validating their efficacy across different cancer types.

CPA4 plays a role in various signaling pathways across different types of tumors. In lung cancer cells [76], circCPA4 can regulate the expression of TGF-β2 by acting as a sponge for miR-214-3p. In colorectal cancer, CPA4 promotes the growth of CRC cells by activating the STAT3 and ERK pathways [11]. Shao et al. found that CPA4 promotes the progression of pancreatic cancer by activating the PI3K/Akt/mTOR signaling pathway, suggesting that drugs targeting this pathway, such as everolimus and temsirolimus, might indirectly inhibit the function of CPA4 [12]. In non-small cell lung cancer (NSCLC), the downregulation of CPA4 inhibits the activation of AKT, subsequently reducing the expression of c-MYC. This change leads to G1 phase arrest in tumor cells, inhibits cell proliferation, and promotes the suppression of tumors by inducing apoptosis [77].

In the last, the downregulation of CPA4 via shRNA in HEC-1-A and Ishikawa cell lines led to decreased cell viability, migration, invasion capabilities, an increase in apoptotic cells, and a cell cycle arrest predominantly in the G2/M phase. These cellular experiment outcomes further corroborate the close relationship between CPA4 and cancer cell proliferation, invasion, and metastasis, positioning CPA4 as a potential molecular target for cancer therapy.

In light of recent literature, such as the comprehensive analysis of CPA4 as a poor prognostic biomarker correlated with immune cell infiltration in bladder cancer [18], it is evident that CPA4's overexpression is associated with shorter overall survival and may influence immune response via markers related to T cell exhaustion. These findings enhance the proposition of CPA4 as a valuable biomarker for the diagnosis and prognosis of endometrial cancer, supporting its potential as a target for therapeutic interventions. The investigation into CPA4's role in endometrial cancer progression is a significant step towards understanding the molecular underpinnings of this malignancy and devising new strategies for its management.

In addition, pathway enrichment analysis identified several key signaling pathways, such as PI3K/Akt, MAPK, and TGF-β, which have been extensively reported to be associated with tumor proliferation, migration, and invasion [12]. In cellular experiments, inhibition of CPA4 resulted in decreased cell proliferation, migration, and invasion, potentially linked to the downregulation of the PI3K/Akt and MAPK signaling pathways. Furthermore, the role of the TGF-β signaling pathway in epithelial–mesenchymal transition (EMT) aligns with previous findings, suggesting that CPA4 inhibition may suppress the EMT process by affecting the TGF-β pathway, thereby reducing the invasive capacity of tumor cells.

These results indicate that CPA4 may influence the progression of endometrial cancer through multiple signaling pathways. However, current research is primarily based on database analysis and functional experiments, lacking further mechanistic validation, especially in vivo studies, which may introduce bias. Future research should focus on verifying the specific roles of these pathways, particularly through in vivo experiments, to explore their functions within the tumor microenvironment.

Future studies should emphasize the use of larger sample sizes and more in-depth pathway enrichment analyses to comprehensively explore the molecular mechanisms of CPA4 in endometrial cancer. Given CPA4's association with multiple key signaling pathways, such as the G-protein-coupled receptor (GPCR) signaling pathway, estrogen signaling pathway, and EMT process, subsequent research should further validate the specific roles of these pathways in CPA4-mediated tumor progression.

Moreover, future research could integrate animal models and clinical samples to evaluate the potential of targeting CPA4-related pathways in the treatment of endometrial cancer. This approach will help clarify the feasibility of CPA4 as a therapeutic target and provide a foundation for personalized treatment strategies.

In summary, the elevated expression of CPA4 is closely associated with the progression, metastasis, and invasion of endometrial cancer, as well as the suppression of immune responses. This suggests that CPA4 could serve as a potential diagnostic and therapeutic biomarker and an independent risk factor for prognosis. Despite its recognized role in cancer, the molecular mechanisms underlying CPA4's function remain poorly understood, particularly in the context of endometrial cancer. Therefore, future research should focus on elucidating the specific biological functions and pathways through which CPA4 contributes to endometrial cancer progression.

Current studies primarily describe the correlation between CPA4 expression and cancer-related phenomena through bioinformatics and cell-based experiments, but the underlying mechanisms have not been thoroughly explored. Specifically, CPA4 may promote cancer cell proliferation, invasion, and metastasis by modulating multiple key signaling pathways. First, CPA4 may regulate cellular behavior via the G-protein-coupled receptor (GPCR) signaling pathway. GPCRs play a crucial role in tumorigenesis, particularly in cancer cell proliferation, migration, and immune evasion. Future studies should investigate whether CPA4 directly or indirectly modulates GPCR activity, influencing cancer cell growth and immune response.

In addition, the enrichment of the estrogen signaling pathway suggests that CPA4 may be involved in hormone-dependent cellular processes. Previous research has shown that estrogen can affect DNA damage repair mechanisms and induce chemoresistance, thereby promoting cancer progression. Therefore, further investigation is needed to determine whether CPA4 interacts with estrogen receptors, modulating DNA repair processes or influencing chemotherapy resistance in tumor cells.

Regarding CPA4's involvement in epithelial-to-mesenchymal transition (EMT), previous studies suggest that EMT is critical for tumor cell migration and invasion. CPA4 may influence this process through the regulation of the TGF-β signaling pathway. Future experiments should explore whether CPA4 facilitates EMT via the TGF-β pathway or other related mechanisms, thereby promoting cancer cell invasion and metastasis.

Although current research has identified CPA4's association with several key signaling pathways, in-depth experimental validation, especially in vivo studies, is lacking. Thus, future research should focus on verifying the molecular mechanisms of CPA4 using animal models and clinical samples. Moreover, larger-scale studies incorporating multifactorial diagnostic models are needed to minimize sample bias and enhance the accuracy of prognostic assessments.

In future investigations, the development of specific CPA4 inhibitors should be a key priority. By leveraging CPA4’s structural and functional characteristics, high-throughput screening and structure-based optimization strategies could lead to the identification of effective CPA4 inhibitors. Such inhibitors could provide novel therapeutic options for endometrial cancer and other CPA4-associated malignancies, ultimately contributing to personalized treatment strategies, including targeted therapies and immune checkpoint inhibitors.