Serum isoenzymes in cancer diagnosis and management.

The 10 isoenzyme markers discussed here represent those that in the author's judgment show promise as effective tumor markers. The relative usefulness of these isoenzymes as tumor markers is summarized in Table 6. Each isoenzyme is evaluated by a rating system, with a scale of 0-5 points in each of seven categories. The hypothetical ideal tumor marker received 5 points in all seven categories for a total score of 35. Unfortunately, less than perfect scores ranging from 9 to 26 were found for the 10 isoenzymes evaluated here. The five best isoenzymes were neuron-specific enolase (26 points), prostatic acid phosphatase (23 points), placental alkaline phosphatase (20 points), thymidine kinase 1 (16 points), and lactate dehydrogenase 1 (16 points). In general, low isoenzyme scores can be attributed to the problems exhibited by all tumor markers: insensitivity to early-stage malignancies and false-positive elevations in nonmalignant diseases. Nevertheless, each of the 10 isoenzymes described here has potential clinical usefulness to support a diagnosis of cancer and/or to assist in the monitoring of therapy.