CEA often fluctuates. We have to give 2 months of chemo before we can assess response. CEA is not enirely reliabnle unless you have done it 3-4 times in a row, one month aprt. Then it will show us a trend for tumor being better or worse. Yet we rely much more on Imaging studies(CT scan etc) along with patient symptoms and doctor's examination. All together(these 4 items) will help us conclude if tumor is getting small.