Cea is rising 1 point per month while on irinotecan. Does this mean not responding to treatment?

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.
CEA and chemo. If the CEA has been used to monitor response to treatment than a rise and a steady rise would mean that cancer is producing the CEA. It might be a good time to actually go back and plot the values to make sure the rise is real. If so a repeat of scans might be in order .