Plasma 5-S-cysteinyldopa correlates with tumor size in melanoma-bearing mice

A sensitive assay method employing high performance liquid chromatography with electrochemical detection (HPLC-ED) was used to compare 5-S-cysteinyldopa (CD) levels in plasma to tumor size in a murine melanoma model system. Plasma CD levels correlated with the sizes of primary tumor masses in mice, and the presence of metastatic tumors did not significantly affect the relationship. Elevated plasma CD levels appear to be directly related to tumor pigmentation: mice who had nonpigmented tumors induced by injections of amelanotic melanoma cells (NP) did not have elevated plasma CD levels. These studies indicate that plasma CD levels may serve as a marker for pigmented malignant melanomas and may be useful in following patients who are at high risk for these tumors.