Sensitivity and specificity curves for the different prognostic factors. The sensitivity (i.e. the number of correctly predicted patients with metastatic spread) and specificity (i.e. the number of correctly predicted patients that did not develop metastases) were plotted on the same axes as a representation of the predictive value of the prognostic test. The point at which the two lines intersect represents the optimal cut-off point for determining a positive or negative test result in order to achieve the best sensitivity and specificity for the test. A) Shields Index B) Breslow thickness for the 4500 patients included in the Frenchay Hospital Melanoma Registry C) Epi-tumoural LD D) AJCC stage.