Alpha-fetoprotein half-life as a predictor of residual testicular tumor. Effect of the analytic strategy on test sensitivity and specificity.

BACKGROUND

Alpha-fetoprotein (AFP) serum values after orchiectomy for testicular cancer can be used to predict the residual disease status. However, the optimal strategy for postorchiectomy marker analysis has not been studied. This article evaluated different analytic methods in an effort to identify the approach that provided the greatest sensitivity and specificity for occult residual disease.

METHODS

Statistical information on the AFP half-life (t1/2) derived from a clinical data set of 24 patients with AFP-secreting clinical Stage A testicular cancer and pathologically defined nodal status was incorporated into a mathematic model of postorchiectomy marker values as a function of residual tumor volume and time. The model was used to test the effect of various analytic strategies on detecting the residual tumor. The clinical data set then was analyzed to measure the effect of different analytic methods on the predictive value of the AFP t1/2.

RESULTS

In the model, the AFP t1/2 calculated from a single set of serum measurements obtained from the initial serum t1/2 was a poor predictor of disease status in patients with up to 40% residual tumor volume. Determined by the sequential addition of serum values obtained at normal t1/2 intervals, the AFP t1/2 improved in sensitivity but required up to seven serial values (35 days) to detect an abnormal t1/2 in patients with 10% residual tumor. By contrast, changes in the most recent interval t1/2 relative to the initial calculated t1/2 predicted the disease status in patients with 10% residual tumor after four t1/2 (20 days) and in patients with 1% residual volume after 35 days.

CONCLUSIONS

The use of this last strategy in the clinical data set improved both the sensitivity and specificity of the AFP t1/2 in predicting residual tumor relative to the other methods.