ID4 and prostate cancer: In addition to prostate cancer, decreased ID4 expression is also observed in leukemia [6], AML [7-11], CLL [12], ALL [13], glial neoplasia [14], squamous cell carcinoma [15], gastric cancer [16], pancreatic cancer [17], colorectal adenocarcinoma [18, 19], malignant lymphoma [20], cholangiocarcinoma [21], Barrett's esophagus and esophageal adenocarcinoma [22] and lung cancer [23].