Background:Programmed cell death protein 4 (PDCD4) is a novel tumor suppressor protein involved in pro?grammed cell death. Its association with cancer progression has been observed in multiple tumor models, but evidence supporting its association with solid tumors in humans remains controversial. This study aimed to determine the clinical signiifcance and prognostic value of PDCD4 in solid tumors. Methods:A systematic literature review was performed to retrieve publications with available clinical informa?tion and survival data. The eligibility of the selected articles was based on the criteria of the Dutch Cochrane Centre proposed by the Meta?analysis Of Observational Studies in Epidemiology group. Pooled odds ratios (ORs), hazard ratios (HRs), and 95% conifdence intervals (CIs) for survival analysis were calculated. Publication bias was examined by Begg’s and Egger’s tests. Results:Clinical data of 2227 cancer patients with solid tumors from 23 studies were evaluated. PDCD4 expression was signiifcantly associated with the differentiation status of head and neck cancer (OR 4.25, 95% CI 1.87–9.66) and digestive system cancer (OR 2.87, 95% CI 1.84–4.48). Down?regulation of PDCD4 was signiifcantly associated with short overall survival of patients with head and neck (HR: 3.44, 95% CI 2.38–4.98), breast (HR: 1.86, 95% CI 1.36–2.54), digestive system (HR: 2.12, 95% CI 1.75–2.56), and urinary system cancers (HR: 3.16, 95% CI 1.06–9.41). Conclusions:The current evidence suggests that PDCD4 down?regulation is involved in the progression of several types of solid tumor and is a potential marker for solid tumor prognoses. Its clinical usefulness should be conifrmed by large?scale prospective studies.