Diagnostic sensitivity, diagnostic specificity and predictive value of the determination of tumour markers

The meaningful use of tumour markers for cancer diagnosis depends on the nature of the diagnostic problem, on an adequate definition of positive and negative test results, and on the correct choice of the patient group. Potential diagnostic applications lie in screening studies, diagnosis in patients with symptoms, staging and prognosis, diagnosis of local recurrence and distant metastases, and the monitoring of radio- and chemotherapy. In quantitative tests, a positive or negative test result may be obtained by the establishment of reference ranges in control groups, or by longitudinal studies in single patients. Usually, the monitoring of therapy and the diagnosis of tumour progression are performed by following the concentration pattern of the marker. When tumour marker determinations are performed in conjunction with other diagnostic tests, the diagnostic sensitivity or specificity may be increased, depending on the particular test combination. The determination of tumour markers with limited diagnostic specificity should be performed in groups of patients with a high prevalence of the disease, e.g. in the postoperative follow-up of patients with a high risk of tumour recurrence. Tumour markers with high diagnostic specificity are also useful in differential diagnosis.