To determine whether plasma 5-S-cysteinyldopa levels are useful in following up patients at risk for melanoma, we measured plasma 5-S-cysteinyldopa in patients with dysplastic nevus syndrome and/or malignant melanoma and in control subjects. In patients with dysplastic nevus syndrome, plasma 5-S-cysteinyldopa levels did not differ from those in control subjects. Conversely, patients with malignant melanomas had significantly higher plasma 5-S-cysteinyldopa levels than did controls. Those with localized cutaneous malignant melanoma and no distant metastases (Stages I and II disease) had 5-S-cysteinyldopa levels twofold greater than those of control subjects, whereas the levels of those with regional lymph node involvement (Stage III disease) were fourfold greater than those of control subjects. Levels of those with extraregional metastases (Stage IV disease) were 7- to 450-fold higher than those of control subjects. Moreover, plasma 5-S-cysteinyldopa levels correlated with the spread of disease and were useful in distmguishing primary melanoma and Stages III and IV melanoma. We conclude that plasma 5-S-cysteinyldopa may be an important tool for identifying melanoma at an earlier, more curable stage and for following up patients at risk for the development of melanoma, for example, those with dysplastic nevus syndrome.
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