Monday, October 1, 2007

Cancer quantified

Since starting treatment more than three years ago, our main measurement of its effectiveness has been the level of carcinoembryonic antigen (CEA) in my blood. CEA is a protein involved in cell adhesion that is normally present in a developing fetus but not in an adult. A plot of CEA versus time shows the history of my cancer's ebb and flow.

A normal CEA level is below 2.5 ng/mL. Higher levels can be produced by gastrointestinal cancers, and levels above 20 ng/mL are associated with metastatic tumors. Note that the vertical scale is logarithmic, not linear, so each major tick is ten times higher than the one below. My CEA was at 23 when diagnosed in August 2004.

Colectomy (removal of the lower colon) and FOLFOX chemotherapy reduced my CEA to normal. A laparoscopic examination showed that I still had many small tumors remaining, so in May 2005 surgeons removed my peritoneum (a membrane covering organs in the abdomen) and diseased parts of many other organs. Then they applied direct, heated chemotherapy to kill any remaining cancer cells.

The surgery seemed successful, but in early 2006 my CEA shot back up to worrying levels. CAT scans and PET scans confirmed that tumors were growing in several spots, particularly around the pelvis. We started chemotherapy with Erbitux and Camptosar, but the cancer kept growing.

In November 2006 we tried the oral chemotherapy Xeloda plus Avastin. The cancer responded well, and my CEA has dropped from a high of 160 ng/mL down to normal. We are continuing chemotherapy since a normal CEA does not necessarily mean that all the cancer is gone. I'll get scans again in a few weeks to see if those have cleared.

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