Can cancer always show up in blood tests?

Not all cancers: Most cancers are not detected in the blood initially. There are a few that produce markers that allow us to screen patients for cancer with a blood test. Prostate cancer is the most common. There are some blood markers that are used to detect GI cancers as well as to follow patients with gyn cancers as well as breast. Testicular cancer also has commonly used markers. Must be in context of case.

NO: Unless you're anemic (low blood count) or have leukemia, basic blood tests won't show cancer. If you have true concerns, perhaps because of family tendencies, speak with your doctor. Good luck