Discordance Analysis Characteristics as a New Method to Compare the Diagnostic Accuracy of Tests: Example of Complexed Versus Total Prostate-Specific Antigen

National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for Use of Tumor Markers in Testicular, Prostate, Colorectal, Breast, and Ovarian Cancers

Background: Updated National Academy of Clinical Biochemistry (NACB) Laboratory Medicine Practice Guidelines for the use of tumor markers in the clinic have been developed.

Methods: Published reports relevant to use of tumor markers for 5 cancer sites—testicular, prostate, colorectal, breast, and ovarian—were critically reviewed.

Results: For testicular cancer, α-fetoprotein, human chorionic gonadotropin, and lactate dehydrogenase are recommended for diagnosis/case finding, staging, prognosis determination, recurrence detection, and therapy monitoring. α-Fetoprotein is also recommended for differential diagnosis of nonseminomatous and seminomatous germ cell tumors. Prostate-specific antigen (PSA) is not recommended for prostate cancer screening, but may be used for detecting disease recurrence and monitoring therapy. Free PSA measurement data are useful for distinguishing malignant from benign prostatic disease when total PSA is <10 μg/L. In colorectal cancer, carcinoembryonic antigen is recommended (with some caveats) for prognosis determination, postoperative surveillance, and therapy monitoring in advanced disease. Fecal occult blood testing may be used for screening asymptomatic adults 50 years or older. For breast cancer, estrogen and progesterone receptors are mandatory for predicting response to hormone therapy, human epidermal growth factor receptor-2 measurement is mandatory for predicting response to trastuzumab, and urokinase plasminogen activator/plasminogen activator inhibitor 1 may be used for determining prognosis in lymph node–negative patients. CA15-3/BR27–29 or carcinoembryonic antigen may be used for therapy monitoring in advanced disease. CA125 is recommended (with transvaginal ultrasound) for early detection of ovarian cancer in women at high risk for this disease. CA125 is also recommended for differential diagnosis of suspicious pelvic masses in postmenopausal women, as well as for detection of recurrence, monitoring of therapy, and determination of prognosis in women with ovarian cancer.

Conclusions: Implementation of these recommendations should encourage optimal use of tumor markers.

New Insights Into the Diagnostic Accuracy of Complexed and Total Prostate Specific Antigen Using Discordance Analysis Characteristics

PURPOSE

Comparison of diagnostic performances of total and complexed prostate specific antigen (tPSA, cPSA) using ROC curve analysis resulted in controversial interpretations. To overcome the biases due to analysis of subgroups selected by concentration ranges of only 1 marker the novel approach named discordance analysis characteristics is presented.

MATERIALS AND METHODS

DAC method includes only patients who are discordantly categorized by the tests under investigation using cutoffs with identical sensitivity. Within those patients parameters describing diagnostic accuracy are calculated. The systematic nature of the results is confirmed by varying the cutoffs. DAC method is demonstrated considering the example of cPSA and tPSA data from 2 prostate cancer studies with a total of 1,624 patients (study A and B, of 283 and 565 with as well as 417 and 359 men without prostate cancer, respectively). PSA concentrations were measured using the Bayer assays.

RESULTS

The DAC method proved that cPSA outperformed tPSA regarding the criteria diagnostic specificity and positive predictive value. Among discordantly tested patients cPSA detected patients with an about 2-fold higher risk to have prostate cancer and with a 3.6 to 5.5-fold better specificity than tPSA. Using cPSA instead of tPSA more than 10% of unnecessary biopsies could be avoided in the tPSA range of 3 to 5 ng/ml.

CONCLUSIONS

The superior diagnostic performance of cPSA in comparison with tPSA warrants the recommendation to use cPSA as initial test in prostate cancer diagnostics. The DAC method is generally recommended to replace comparative ROC analyses of subgroups to evaluate the diagnostic usefulness of markers.