While there may be different reasons for the CEA to go up, I will share that my CEA skyrocketed during chemotherapy. I was taking an oral chemo drug (Capecitabine) and received 4 rounds of infusions (Oxilaplatin). It shot up to 12.9. As soon as I finished with chemotherapy, it started to drop gradually every 3 months--down to 7 something then 4 something, 3 something and now the last blood work showed 2.3. My oncologist did not commit to any reason but did agree that inflammation could cause the rise.I consulted with another oncologist I had previously spoken with and he said the capecitabine could cause the inflammation/spike in CEA. The internet also has studies that show ocaliaplatin can cause a rise in the CEA. The spike in CEA during chemo is not common--I think it's about 10%--but according to the internet (not a reliable source) it infers a better prognosis when this happens. I think a helpful way to deal with it is to know there can be multiple causes of a rising CEA.