The term "tumour markers" embraces a spectrum of molecules of widely divergent characteristics, but sharing an association with malignancy that facilitates their application in the clinical detection (diagnosis, screening) and management (monitoring, prognosis) of cancer patients (Table 1).

Tumour markers are generally not diagnostic, although they can provide information that may contribute to the diagnostic process, particularly in selected patients (e.g. those referred to specialist hospital units). For pre-treatment tumour marker measurements in patients with suspected malignancy, clinical presentation will usually suggest which markers may be most helpful (Table 1). The diagnostic value of a tumour marker will depend on the prevalence of the disease in the population group being considered, and on the sensitivity and specificity of the tumour marker, which may be defined as follows:

Specificity: The percentage of normal persons or persons with benign conditions for whom a negative result is obtained. The greater the specificity, the fewer the false-positives.

Sensitivity: The percentage of test results which are correctly positive in the presence of a tumour. The greater the sensitivity, the fewer the false-negatives.

Tumour markers may be helpful in differential diagnosis (e.g. in germ cell cancers where they may be different cell types) and especially where there are metastatic deposits but the primary site is unknown (e.g. NSE in lung cancer, CA15.3 in breast cancer).

It is important to remember that no tumour marker is specific for malignancy (elevation may be due to other malignancy, or to benign disease), and that a "normal" tumour marker result never necessarily excludes malignancy or recurrence.

It is well-documented that serial monitoring of serum tumour marker concentrations post-therapy may provide early indication of recurrence, sometimes months before this is clinically evident. Unless alternative therapy is available and can be instituted on the basis of marker results, such lead time may not benefit the patients. However, early awareness of recurrence may in some cases avoid alternative and more expensive investigation (e.g. diagnostic imaging). The possibility of early intervention on the basis of marker rise, although not yet widely implemented in routine practice, requires investigation, through randomised controlled trials.

Many tumour marker tests were formerly performed in specialist laboratories, but with the development of automated immunoassays, they are now often available in routine laboratories. Results are consequently more readily available to non-specialist clinicians, who may be less familiar with their interpretation.

This, coupled with increasing pressure on laboratories to reduce costs, and on clinicians to practice "evidence-based medicine", encourages critical appraisal of how to achieve best use of these tests. This is being undertaken by numerous groups, including the European Group on Tumour Markers. Conclusions reached by its Focus Groups are summarised in the following papers. General recommendations about quality requirements for tumour marker measurements will be summarised first, before discussing recommendations about how tumour markers should best be used for different malignancies. The order of the papers is as indicated below:

• Quality requirements and control
• Germ cell cancer
• Prostate cancer
• Breast cancer
• Gynaecological cancer
• Gastrointestinal cancer
• Lung cancer

 

TABLE 1. Characteristics of tumour markers discussed in these articles

Back