Which tumor markers are considered to be reliable indicators for cancer?

Tumor markers are in short, not reliable indicators for cancer. They are proteins produced by cancer cells and normal cells. Therefore they are always measurable in someone's blood tests and will never have a zero value. They are, however, included in most health screening packages, and therefore helpful when interpreted in conjunction with other parameters, as well as the patient's signs and symptoms. This will help guide subsequent investigations towards a particular organ system should the related tumor marker appear elevated. It is not uncommon for someone to have abnormal tumor markers and yet no cancerous cause is found despite multiple investigations. In such cases, they should be monitored initially for any rising trends.