Depends on what bloodwork you're talking about. Certain blood tests are for cancer markers, such as CA125 or PSA...if those are going up in a cancer patient who is receiving treatment, then it usually means that the treatment isn't working.
But there are so many blood tests that are done for various reasons...for example, they may test creatinine levels to make sure the kidneys aren't being affected by treatment, or liver enzymes...and on and on. We'd really need to know not only which test is elevated, but what type of cancer the patient has and what their treatment is to give any kind of definitive explanation.
