The situation: My SO’s mother had a bout with cancer. It wasn’t too serious, as these things go: a small tumor, easily removed, with a six-month round of light chemo. The blood tests in her regular checkups were coming up clean, the latest was less than a month ago. Now she has some more health problems and the doctor thinks the cancer may have returned. Biopsies have been ordered, and the results will be back by the end of the week.
The questions:
How does a blood test detect cancer? What are they looking for? Is it possible to have a clean blood test and then less than a month later have a relapse?
Medical dopers, please educate me.
With certain cancers, certain proteins are put into the bloodstream. These are often proteins that are tissue specific and are not usually released into the bloodstream. With cancer, there is increased cell growth and often increased cell death due to the cancer outgrowing blood supply and necrosing. These tissue specific factors can be detected with an ELISA or a Western Blot – antibodies against those proteins are used to detect their presence. The most famous is a PSA – prostate specific antigen. Elevated levels of PSA are sometimes indicative of prostate cancer, although it is not specific for cancer. Other markers are CA125 (ovarian, lung, cervical, uterine) and AFP (liver and testicular), although there is a whole set.
http://www.vh.org/adult/patient/cancercenter/tumormarker/
Most of these tests are relatively sensitive but not specific (there are a lot of false positives) and are mostly used in conjunction with clinical findings or other tests.
I do blood tests for cancer every day at work, but they’re of a little different type than the kind edwino is talking about. In my case, we do genetic tests.
Many cancers (especially certain leukemias and lymphomas) are associated with translocations, which are when two chromosomes swap chunks of DNA. This can lead to the inappropriate expression of genes that encourage cell growth, which can lead to cancer. So in my lab, we test for these translocations, which helps doctors figure out what kind of cancer it is, which in turns helps them figure out the best way to treat them.