Can a blood test detect cancer?

Only a few cancers. Unfortunately, there are very few cancers that can be detected through blood tests. These include prostate cancer and leukemia. Some other cancers have tumor marker tests, such as breast cancer, ovarian cancer, colon cancer, pancreatic cancer, and others but these are to monitor, not detect the cancer.
Depends. Certain cancers, like colon and pancreatic may have positive "tumor markers", but it depends on cancer types.

Related Questions

Can a blood test detect cancer?

Not really. The only blood test that indicates cancer is psa for men with prostate cancer. Unfortunately, we don't have any 'blood cancer test'. This might be available in the future. Read more...
Yes. However the best way to diagnose cancer is to go to your doctor and have an examination. Blood tests can give clues to how well your organs are functioning and what is happening inside of your body. Read more...

Can doctors detect if you have had any radiation xrays?, in a test like blood or other. Can a blood test detect any cancer?

No and Maybe. There is no test that can see if you have been exposed to X rays. Some blood tests can detect cancer: a complete blood count can detect leukemia. Some substances secreted by tumors can be detected in the blood, but this is not a powerful or precise way of finding cancers in general. biopsy of tissue or collection of tissue or direct visualization is a much better method. Read more...