Biochemical assays for tumor associated enzymes, hormones and other tumor markers in blood are not diagnostic but help in determining effectiveness of therapy.
Carcinoembryonic antigen (CEA) is considered as tumor markers and is raised in various tumor but it is also raised in various other benign conditions. Therefore, Raised concentration of CEA in blood is not a hallmark of Cancer.
Causes of high level of Carcinoembryonic antigen in Blood:

1) Malignant tumors:
a) Breast cancer
b) Colorectal carcinoma.
c) Gastric cancer
d) Pancreatic cancer

2. Benign conditions
a) Hepatitis
b) Alcoholic cirrhosis of liver
d) Crohn's disease
e) Ulcerative colitis
f) Healthy smokers