Cancer is a complex disease that involves abnormal cell growth and proliferation. Many genes and signaling pathways contribute to the development and progression of cancer. SMAD4 is a tumor suppressor gene critical to the TGF-β signaling pathway, which controls cell growth, differentiation, and apoptosis [18].

One of the first indications of SMAD4's involvement in cancer was observed in colorectal cancer [18]. Studies have shown that SMAD4 is frequently mutated or deleted in colorectal tumors. Loss of SMAD4 function in colorectal cancer leads to dysregulation of the TGF-β signaling pathway, promoting tumor growth and metastasis [19]. Moreover, SMAD4 inactivation is associated with poor prognosis and resistance to specific chemotherapeutic agents in colorectal cancer patients [20].

In pancreatic cancer, SMAD4 alterations are even more prevalent, with nearly 55–60% of cases showing SMAD4 gene mutations or deletions. Loss of SMAD4 function is associated with aggressive tumor behavior, increased invasiveness, and resistance to treatment. SMAD4 acts as a pancreatic tumor suppressor by regulating cell cycle control, cell proliferation, and apoptosis. Therefore, abnormalities in SMAD4 contribute to the development of pancreatic cancer and its poor prognosis [21].

Apart from colorectal and pancreatic cancers, dysregulation of SMAD4 has also been observed in other malignancies. SMAD4 gene alterations have been documented in gastric cancer, lung cancer, ovarian cancer, and others. In these tumors, SMAD4 inactivation has been linked to tumor progression, metastasis, and decreased patient survival. These findings highlight the universal importance of the SMAD4 gene in various types of cancer. Given the critical role of SMAD4 in tumor suppression, targeting SMAD4 or the TGF-β signaling pathway holds promise as a therapeutic strategy [22]. Several approaches are being explored, including the restoration of SMAD4 function, inhibition of TGF-β signaling, and combination therapies. Gene therapies, such as gene replacement or targeted SMAD4 reactivation, are being investigated to restore the normal function of SMAD4 in cancer cells. Small molecule inhibitors and monoclonal antibodies targeting TGF-β receptors or downstream effectors are also being developed to block aberrant TGF-β signaling in tumors [23].

As the critical role of SMAD4, we comprehensively explored the molecular characteristics. In colorectal cancer, we found that patients with mutations in the SMAD4 gene had a worse prognosis than those without mutations. It is suggested that SMAD4 mutation results in the loss of cancer inhibitory effect. Tumor mutation load was elevated in patients in the SMAD4 mutation group compared with the unmutated group, implying that patients carrying SMAD4 mutations may be more likely to benefit from immunosuppressive therapy [24]. SMAD4 mutation status may serve as a predictor of sensitivity to immunosuppressive agents in patients with colorectal cancer.

The mutation profile of patients in the SMAD4 mutation group was significantly different from that of patients without SMAD4 mutations, and mutations in the SMAD4 gene may affect the mutation status of other genes [25]. Future studies are necessary to delve deeper into the role of SMAD4 mutations in somatic mutations.

Using single-cell sequencing data and tumor microenvironment immune infiltration analysis, we found that the tumor microenvironment of the patients changed significantly after the SMAD4 gene mutation. There was a significant difference in immune gene expression between the two groups. It is suggested that SMAD4 gene mutation can dramatically affect the immune status of the patients [26]. The CD4 + memory T cells were elevated, and the number of plasma-like dendritic cells was reduced [19]. At the same time, the differential gene enrichment analysis of the two groups suggested that multiple immune-related signaling pathways were altered. Multiple immune-related genes were also limited, and these changes indicated that SMAD4 gene mutations significantly affected the immune status of colon cancer patients [27].

We deeply analyzed the relationship between SMAD4 gene mutation status and drug sensitivity. We found that multiple monoclonal antibody drug sensitivities were altered between the two groups. This has implications for the treatment regimen of patients carrying mutations and is expected to lead to individualized medication for patients. We hope that these studies will be of assistance to clinicians.

However, it is undeniable that our study could be better. First, although we collected sequencing data from TCGA and GEO databases, the amount of these data still needs to be more significant for extensive data validation. There may be issues with sequencing data selection bias and poor representation of patient cohorts. Second, this study was only supported by bioinformatics analysis, and experimental support is needed further to clarify the mechanism of SMAD4 mutations in colorectal cancer. In the follow-up study, we will collect colorectal cancer tissue specimens from clinical patients and verify the conclusions obtained in this study by HE staining, PCR, Western Blot and immunohistochemical staining. If sufficient funds are available, we will consider constructing SMAD4 mutated colorectal cancer cells and mouse models to validate the molecular mechanism further. We will construct different mutants in cancer cell lines to explore the role of SMAD4 mutants in colorectal cancer. In addition, mice with SMAD4 mutations will be bred for further study.