PDCD4 and malignant urinary system neoplasm: Down-regulation of PDCD4 was significantly 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).