If "tumor markers" are not very useful in finding cancer, why do doctors test blood for "tumor markers"?

Screening & FollowUp: Tumor markers can be positive for other reasons than cancer but are never "normally" high, so used as a screening test they can alert us to a potential cancer or other condition which needs more investigation. The hope is to catch a cancer in an early and more treatable phase. Also, for some cancers they can be markers if the effectiveness of therapy or of recurrence.

By all: Guidelines, they should not. It is a sign of misguided good intent, but leads to worry and a wild goose chase. Some say it is because insurance pays for it, and if we were more involved, we would not want to waste limited dollars on unrewarding tests. Others says patients demand and want reassurance. Huge controvery with psa, prostate specific, but not cancer specific, may define early.