MUC5AC and digestive system carcinoma: For the cancer type subgroup analysis, patients with biliary carcinoma (pooled HR: 1.83, 95% CI: 1.269–2.639, P = 0.001) and gastrointestinal carcinoma (pooled HR: 1.44, 95%CI: 1.069–1.949, P = 0.017; details show in Figure 3) had poorer prognoses if they hyper-secreted mucin 5ac, and no heterogeneity was found within these groups (indicating that the cancer type difference might contribute to heterogeneity in the overall meta-analysis; details shown in Figure 3).