COMT and melanoma: On the other hand, minor amounts of those precursors may leak into the bloodstream because of defective membranes surrounding abnormal and incomplete melanosomes in melanoma cells that could facilitate the leakage of 5SCD into the cytosol as partly O-methylated derivatives formed by catechol-O-methyl transferase (COMT) in the liver, and excreted into the blood or urine [51] (Figure 1).