Hi,
I am pretty aware of the tumor marker thing bec. they have been tracking my father's every 2 weeks, trying to determine if his cancer is back. The 2 markers they use for EC are CA 19-9 and CEA. These are really primarily used for other GI cancers (pancreatic and colon I believe), but they generally work for EC as well. There is no marker that is totally specific to EC, so they use these as they seem to correlate with all GI cancers. I do not believe they check them as part of your weekly chemo blood check, but rather periodically to see if your treatment is working. There are other reasons they could go up (other benign GI disorders, inflammatory bowel disease, liver and gall bladder disease, and some lung disease) so if they are going up, it does not NECESSARILY mean the cancer is growing. Unfortunately, in my father's case it did. Here are some links with more info - hope this helps.
Courtney
http://www.aafp.org/afp/20030915/1075.html
http://www.cancer.org/docroot/PED/content/PED_2_3X_Tumor_Mar