Treatment related blood work is one issue...as various poisons, (radiation and chemotherapy), alter our bodies in negative ways. A look at your blood is a look at the physical system overall, and how well it is tolerating the treatment. This type of blood work has little to do with disease. Then there are tests which identify infectious agents, or the process of immune response to infections, both viral and bacterial. These either find the agent itself or show irregular proportions of the normal elements of the blood, the most obvious being white cells and other macrophages, which indicate that an immune response to something is going on. What that response is to, isn't specific, but that something is happening and your body is responding to it, is something that becomes evident, by looking at the balance of normally occurring elements of the blood. But in the realm of cancers, they are usually looking for tumor-associated antigens, or tumor specific antigens (TSA's). Some TSA