Carcinoembryonic antigen (CEA) is significantly elevated, mainly seen in gastrointestinal tumors, especially in colorectal cancers such as colon and rectal cancers, where CEA elevation is more pronounced. It can also be notably higher in patients with lung adenocarcinoma, and bladder cancer might show an increase in CEA as well. However, the increase in CEA is not necessarily consistent, and its diagnostic value for bladder cancer is limited due to low specificity and sensitivity, making it not very instructive. The definitive diagnosis of bladder cancer primarily involves cystoscopy and taking a biopsy to confirm the presence of cancer.