Clinical protocols for the application of tests for circulating tumor markers

Circulating marker level determination in clinical practice requires an adequate strategy of application, in view of the particular features of the parameter related to the marker. The test result, which is usually expressed in terms of concentration, cannot be considered as an absolute value because every biochemical tumor indicator expresses an activity of the tumor which generally leads to increased levels of a "normal" substance in blood or biological liquids. Therefore, the result should be interpreted as a dynamic variation occurring in time, and should always be related to a previous reference value. This means that marker determination in clinical practice should be repeated periodically, both for the evaluation of tumor response to treatment and for the detection of recurrence after radical surgery. A single measurement at the time of disease presentation can characterize the tumor with regard to its capacity of producing the signal, and consequently regarding its extent and growth. These laboratory findings are of no value whatever if they are not integrated with all the other available clinical and instrumental data concerning the neoplasm; only then can they provide useful additional information. Also, all biological variables should be taken into account which may affect circulating marker levels independently of the history of the tumor such as sex, age, clearing organ function, race, alcohol and tobacco habits, concomitant diseases. These procedural protocols should be outlined and codified for each individual neoplasm since it is useless to work with scattered data which are not ordered in some kind of procedural logic.(ABSTRACT TRUNCATED AT 250 WORDS)