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Melanin is a heterogeneous pigment produced within melanosomes
of melanocytes through the melanogenesis pathway. The two major forms are
eumelanin, a brown-black pigment with generally
photoprotective and antioxidant properties, and pheomelanin,
a yellow-red pigment that is less photostable and can contribute to oxidative
stress under some conditions. In normal skin, melanin protects against
ultraviolet-induced DNA damage. In melanoma, however, active melanogenesis and
high tumour pigmentation can have complex effects: melanin and melanogenic
intermediates may promote oxidative stress, metabolic adaptation,
immunosuppression and resistance to radiotherapy, chemotherapy or immunotherapy,
while melanin can also suppress some metastatic processes and protect cells
from oxidative injury. Therefore, melanin should be classified as a
context-dependent melanoma biomarker and melanogenesis target
rather than assigned a universal cancer-associated direction.
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