A substance being studied in the treatment of melanoma and many other types of cancer. D-1MT blocks the breakdown of the amino acid tryptophan, which is needed for T cells (a type of immune system cell) to kill tumor cells. Giving D-1MT to patients who have received chemotherapy for cancer may help kill more tumor cells. It is a type of enzyme inhibitor and immunosuppressant. Also called 1-methyl-d-tryptophan.