One of the most commonly used markers, the Ki-67 protein (MIB-1), is expressed during the interphase and mitotic phases of the cell cycle (G1, G2, S, M) and is absent in the G0 phase, making it a useful marker to differentiate an actively proliferating melanoma from a quiescent melanocytic nevus (69). The gene discussed is MKI67; the disease is melanocytic nevus.