What are tumor markers, and does having them mean that I have cancer?

Blood tests. Tumor markers are blood tests that are sometimes used to follow progression of cancer once it has already been diagnosed. We rarely, if ever, use tumor makers to make a cancer diagnosis. There are many other reasons why these markers may be elevated including inflammation, infection, etc.
Testis Cancer has. Reliable tumor markers (tm): Alpha feto-protein and hcg. None of the others (cea, ca 125, ca 19 9 etc) are diagnostic or used in screening, and are weakly correlated with response AFP & HCG are well correlated with response or progression. Tm's should be done rarely if at all. They are costly and provide uneiable information.
Tumor markers. A term to just describe all the things you might find if cancer is present. Can be a substance like CEA or certain gene mutations seen in cancer cells when dna is analyzed. Many are normal in low concentrations, but not high ones. If your levels are high then your physician will start looking for tumors or have confirmed one. If normal, then less-concerned.