In the current study, cellular metabolic states determined using a Seahorse bioanalyzer and phenotypes determined according to 3D spheroid forming efficacy were significantly modulated by a specific inhibitor of MITF activity in a concentration-dependent manner, and they were also different among the MM cell lines A375, WM266-4, and Skmel-24 as well as between the parent A375 cells and the anti-tumor drug-resistant A375DT cells. The gene discussed is MITF; the disease is Miyoshi myopathy.