Table 3.

A tumor marker can be classified according to six different clinical criteria such as biochemical characteristics, organ specificity, or clinical usefulness in order to assess the value of tumor markers in clinical practice

Is serum YKL-40 a tumor marker?
1. “The marker is produced exclusively by specific tumor cells (tumor specific)”No
2. “The marker is absent in healthy or benign disease (high specificity)”No
3. “The marker is present frequently in the targeted malignancy (high sensitivity)”No
4. “The marker is detectable in early stage subclinical disease (useful for screening)”+/−
5. “The marker's concentration reflects prognosis for an individual patient (prognosticator)”+
6. “The marker's degree of expression correlates with therapeutic results (useful for monitoring)”+/−
  • NOTE: Tumor markers classified according to Werner et al. (100). (+/−), utility scale defined by Hayes et al. (101, 102): data are suggestive that the marker may correlate with biological process and/or biological end point, and preliminary data suggest that use of the marker may contribute to favorable clinical outcome, but more definite studies are required. Thus, the marker is still considered highly investigational and should not be used for standard clinical practice. (+), utility scale defined by Hayes et al. (101, 102): sufficient data are available to show that the marker correlates with the biological process and/or end point related to the use, and that the marker results might affect favorable clinical outcome for that use. However, the marker is still considered investigational and should not be used in the standard clinical setting for one of three reasons: (a) the marker correlates with another marker or test that has been established to have clinical utility, but the new marker has not been shown to clearly provide any advantage, (b) the marker may contribute independent information, but it is unclear whether that information provides clinical utility because treatment options have not been shown to change outcome, and (c) preliminary data for the marker is quite encouraging, but the level of evidence is lacking to document clinical utility.