The monitoring role of plasma CEA alone and in association with other tumor markers in colorectal and mammary carcinoma.

During the past decade, evidence has accumulated to show that most, if not all, human tumors produce a variety of different factors which, if they pass into the blood and/or urine, may serve as tumor index substances (tumor markers).7 Tumor markers may either be: 1) tumor-derived--i.e., produced by the tumor itself, or 2) tumor-associated--i.e., produced by other tissues in response to the presence of the tumor and its local or distant effects on that tissue. Examples of this latter category include the changes in urinary hydroxyproline output in patients with bone metastases or the altered levels of serum acute phase proteins in neoplasia in general.7 Tumor-derived markers may be produced by either the tumor cell population itself, e.g., CEA, alpha-fetoprotein (AFP), and other oncofetal antigens, inappropriate hormones such as ACTH etc., or by their supporting framework (stroma), e.g., the osteolysins of human breast cancer.3