S1P receptor modulators (S1P-RM) are oral disease-modifying therapies (DMTs) for multiple sclerosis (MS). Several authorities have raised doubts that S1P-RM are responsible for an increased risk of melanoma in patients with MS. We studied the in vitro effects of S1P-RM on different melanoma cell lines to compare the effect of available S1P-RM on the proliferation of human melanoma cells.