Prognostic role and clinicopathological features of SMAD4 gene mutation in colorectal cancer: a systematic review and meta-analysis

Background Approximately 5.0%-24.2% of colorectal cancers (CRCs) have activating mutations in SMAD4, making it one of the frequently mutated genes in CRC. We thus carried out a comprehensive system review and meta-analysis investigating the prognostic significance and clinicopathological features of mutation of SMAD4 gene in CRC. Methods A detailed literature search was conducted in PubMed, Web of Science and Embase databases to study the relationship between mutations of SMAD4 gene and the demographic and clinicopathological characteristics in patients with CRC. The hazard ratios with 95% confidence intervals were used to evaluate the effect of SMAD4 mutations on overall survival (OS) and progression-free survival (PFS)/recurrence-free survival (RFS).Results Ten studies enrolling 4394 patients were eligible for inclusion. Data on OS were available from five studies. Comparing SMAD4-mutated CRC patients with SMAD4 wild-type CRC patients, the summary HR for OS was 1.46 (95% confidence interval [95% CI] 1.28–1.67, P=0.001), the summary HR for PFS/RFS was 1.59 (95% CI=1.14–2.22, P=0.006). In terms of clinicopathology parameters, SMAD4 mutations were associated with tumor location (odds ratio [OR]= 1.15, colon/rectum, 95% CI=1.01-1.31, P=0.042), TNM stage (OR=0.78, stage Ⅰ-Ⅲ/Ⅳ, [95% CI] 0.63-0.97, P=0.025), lymph node metastases (OR=1.42, N+/N0, 95% CI=1.20-1.67, P<0.001), mucinous differentiation (OR=2.23, 95% CI=1.85-2.70, P<0.001) and rat sarcoma viral oncogene homolog (RAS) status (OR=0.47, RAS wild-type/RAS mutation, 95% CI=0.30-0.73, P=0.001). No connection was found with age, gender, tumor grade, microsatellite instability (MSI) status and b-viral oncogene homolog B1(BRAF) status. Besides, publication bias was not observed in all studies.Conclusions This meta-analysis suggests that SMAD4 mutation was associated with OS, PFS/RFS, and clinicopathological parameters, including tumor site, disease stage, RAS status, lymph node metastases and tumor mucinous differentiation. It was indicated that SMAD4 mutations could predict the poor prognosis and aggressive clinicopathological characteristics of CRC. More large-sample cohort studies were needed to further confirm this conclusion. As SMAD4 mutation was found to be closely associated with RAS mutations, their relationship was worth further investigating.

P118 LOSS OF SMAD4 EXPRESSION IN ESOPHAGEAL ADENOCARCINOMA (EAC) IS CORRELATED TO POOR SURVIVAL

Aim Our study is aimed to evaluate the impact of SMAD4 expression on the clinical outcome of therapy for esophageal adenocarcinoma (EAC). Background & Methods Esophageal adenocarcinoma is characterized by a high genetic heterogeneity and a low survival rate, despite the adoption of aggressive therapies. We evaluated the expression of SMAD4, a tumor suppressor gene frequently mutated in cancer. by immunohistochemistry in 67 formalin-embedded (FFPE) EAC surgical specimens (patients were primarily treated with surgical resection-naïve cases), 34 of which were analyzed for SMAD4 gene by Next Generation Sequencing (NGS) with a dedicated target panel. Loss of SMAD4 protein was defined by a complete loss of expression in least 30% of cancer cells. Survival curves were determined using Kaplan–Meier methods. Results Loss of SMAD4 immunoreactivity was found in 33 out of 67 EAC cases (49.3%). Among a subset of 34 cases assessed in NGS, SMAD4 mutations were found in 3 cases (8.8%), all associated with protein loss. Loss of SMAD4 expression was also found in several cases with no mutations in SMAD4 gene (17/34, 50%). Loss of SMAD4 immunoreactivity was associated with poor overall survival (p=0.013) and higher risk of recurrence (p=0.001). Conclusion Loss of SMAD4 expression was a recurrent event in EAC, linked with genetic mutations in few cases, whereas in the majority of cases it might be related to epigenetic mechanisms, such as promoter hypermethylation. SMAD4 loss was strongly associated with recurrence and poor survival in patients, suggesting SMAD4 expression as potential prognostic biomarker in EAC. Further studies are required to develop strategic therapeutic options directly targeting SMAD4 and/or its regulators.

Integration of Bioinformatics Resources Reveals the Therapeutic Benefits of Gemcitabine and Cell Cycle Intervention in SMAD4-Deleted Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most common and aggressive type of pancreatic cancer. The five-year survival rate of PDAC is very low (less than 8%), which is associated with the late diagnosis, high metastatic potential, and resistance to therapeutic agents. The identification of better prognostic or therapeutic biomarker may have clinical benefits for PDAC treatment. SMAD4, a central mediator of transforming growth factor beta (TGFβ) signaling pathway, is considered a tumor suppressor gene. SMAD4 inactivation is frequently found in PDAC. However, its role in prognosis and therapeutics of PDAC is still unclear. In this study, we applied bioinformatics approaches, and integrated publicly available resources, to investigate the role of SMAD4 gene deletion in PDAC. We found that SMAD4 deletion was associated with poorer disease-free, but not overall, survival in PDAC patients. Cancer hallmark enrichment and pathway analysis suggested that the upregulation of cell cycle-related genes in SMAD4-deleted PDAC. Chemotherapy response profiling of PDAC cell lines and patient-derived organoids revealed that SMAD4-deleted PDAC was sensitive to gemcitabine, the first-line treatment for PDAC, and specific cell cycle-targeting drugs. Taken together, our study provides an insight into the prognostic and therapeutic roles of SMAD4 gene deletion in PDAC, and SMAD4 gene copy numbers may be used as a therapeutic biomarker for PDAC treatment.