New insight into the role of SMAD4 mutation/deficiency in the prognosis and therapeutic resistance of pancreatic ductal adenocarcinomas

Pancreatic ductal adenocarcinoma (PDAC) patients have an unfavorable prognosis and disappointing treatment outcomes because of late diagnosis, high chemotherapy resistance, ineffective adjuvant chemotherapy, unavailable molecular targeted therapy, and profound immunosuppressive effects in the tumor microenvironment (TME). There are a variety of critical driver proteins, such as KRAS, TP53, PTEN and SMAD4, putatively involved in PDAC etiology. Current knowledge of their molecular mechanisms is still limited. SMAD4 gene alterations in ∼55 % of patients emphasize its key role in PDAC progression, metastasis, resistance and immunity. Despite extensive studies on the TGF-β/SMAD pathway, the impact of SMAD4 mutation/deficiency on PDAC prognosis and treatment, especially its mechanism in drug resistance, has not yet been elucidated. This review summarizes the latest advances in the effect of SMAD4 deficiency on the prognosis and therapeutic resistance of PDAC patients. It might be a predictive and prognostic biomarker or therapeutic target to achieve the desired clinical benefits. Moreover, we discuss potential strategies to implement targeted therapies in terms of SMAD4 genetic status.