Which of the following statement(s) is/are correct with regard to the use of carcinoembryonic antigen (CEA) determinations in management of colorectal cancer?

b. CEA levels are increased in 20% of patients with local recurrence after resectional therapy

c. CEA measurements are increased in 90% of patients with disseminated disease

CEA is a glycoprotein that was originally described to be a tumor-specific antigen derived from neoplasms of the gastrointestinal tract. CEA is an oncofetal antigen because it is also expressed by early embryonic or fetal cells. It is now known that CEA is not tumor-specific since it can be elevated by a variety of malignancies from different sites as well as in some benign conditions. CEA is not useful as a screening or diagnostic test but is useful as a tumor marker. CEA is elevated in over 90% of patients with disseminated colorectal cancer and in about 20% of patients with localized disease. Serum levels generally are elevated in proportion to the mass of the tumor present and often correlate with response to therapy. CEA levels are useful when elevated levels fall to normal levels after curative resection. In about two thirds of patients with recurrent disease, an increased CEA level is the first indicator of the tumor, and serial CEA testing, combined with regular physical examinations, is one of the most useful tests for detecting recurrent colorectal cancer.