Melanin synthesis is a
biologic property unique to the melanocyte. It is highly elevated in
malignant melanoma with the production of both
eumelanin (brown/black pigment) and
pheomelanin (yellow/red pigment), dihydroxyindole (DHI) and
cysteinyldopa (CD), respectively, being major precursors.
Melanin metabolites are often released in the urine of patients with disseminated
melanoma metastasis (melanuria). To establish a better method for the detection of occult
melanoma this study compares the plasma levels of a
pheomelanin metabolite, 5-S-CD, and a
eumelanin metabolite,
6-hydroxy-5-methoxyindole-2-carboxylic acid (
6H5MI2C), in
melanoma and non-
melanoma patients and correlates them with
tumor thickness and
melanoma metastasis. We found a) that the normal plasma levels of 5-S-CD and 6H5M12C are less than 2.22 ng/ml and 1.04 ng/ml, respectively; b) that the group with the normal
6H5MI2C plasma level does not have any
metastasis, whereas a normal 5-S-CD level is seen in both non-
melanoma and
melanoma patients with and without
metastasis; c) that a high plasma
6H5MI2C level is seen in all
melanoma patients with
tumor thickness more than 3.0 mm regardless of the presence or absence of
metastasis, whereas in thinner
melanoma patients this is seen only in positive
metastasis group; and d) that all
melanoma patients with positive
metastases showed a high plasma
6H5MI2C level (more than 1.75 ng/ml). We conclude that the measurement of plasma levels of
melanin metabolites provides a method for detecting occult
melanoma metastasis and estimating the prognosis of
melanoma patients, plasma
6H5MI2C level being more sensitive and reliable than that of 5-S-CD, and its increased level being a high risk factor.