CEA and the Oncoscint Scan

Li Liu
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
I am hoping that you will be able to steer me in the right direction. I am a 26 year old female diagnosed with stage 3 rectal cancer in '96. My CEA has risen in the past 4 months from 0.4 to 3.7, to 5.8 and I am wondering what resources are available as to the validity of the CEA/and or what other factors may contribute to a rise in this lab value.

What I want to know are two things:

  1. What is the validity and usage of the CEA?
  2. How reliable is the Oncoscint scan when looking for current disease?
Any information you can provide me with concerning either method of screening would be very helpful.  
Thank you.

Li Liu, MD OncoLink Editorial Assistant, responds:

Dear B,
Thank you for your interest and question.

Carcinoembryonic antigen (CEA) is one of the oncofetal proteins which is at its highest normal levels during embryonic or fetal life and may re-arise with some malignancies, such as breast, colorectal, pancreatic, lung, and ovarian cancer. Non-malignant diseases that may cause elevation of CEA include cirrhosis, chronic obstructive pulmonary disease, and smoking. Following treatment for colorectal cancer, serial CEA measurement is thought to be the most sensitive lab test of recurrent cancer. Although, the potential therapeutic benefit of postoperative CEA monitoring remains controversial due to potential costs and questionable long term effectiveness.

Given your history of stage III rectal cancer in 1996, a rising CEA level is very concerning. The exact cause of the elevation may never be determined, but steps to rule out recurrent rectal cancer would be appropriate. Oncoscint and CEA-Scan were developed a few years ago and currently are available for the detection of colorectal carcinoma, especially recurrent disease. Oncoscint uses Indium-111 labeled B72.3, which is a murine monoclonal antibody to bind Tag-72. Tag-72 is a cell-surface antigen, which is expressed by colorectal carcinoma cells. The CEA scan uses Technetium-99m-labeled fragment of the anti-CEA antibody for the detection of pelvic recurrence of colorectal carcinoma. Both methods have been used in addition to the conventional diagnostic methods, including CT scan and MRI. However, the exact roles of these two immunoscintigraphical studies remain controversial and need to be defined. The accuracy of Oncoscint is about 70% based on early clinical experience. Exploratory laparotomy often times is required to obtain definitive diagnosis and resect the recurrent disease whenever feasible.