Can blood tests indicate the presence of cancer? i am quite worried that i have cancer, however i have had numerous blood tests (full cbc with diff, tumor marker, thyroid, etc) all coming back normal

Blood test : The only true and diagnostic way of telling if you have cancer is not by blood test, images, CT scans. The only way is by biopsy of the tissue of concern either by CT guided, FNA, or surgical resection. By doing this a pathologist can determine the severity and aggressiveness of the cancer and specifically the type of cancer so an oncologist can modify chemotherapy to target the cancer type.

Not really: Blood tests may be able to suggest or provide evidence against the presence of cancer, but generally cancers are found by pursuing testing or imaging based upon the history and physical exam. At your age the only screening tests for cancers you need should be breast, colon and if a long term smoker- lung CA.