C4A and melanoma: Considering the pivotal role of tumor cells in melanoma, we reexamined 47,047 melanoma cells and discerned five distinct subtypes (Figure 2A): the C0 subtype, characterized by elevated TYRP1 expression; the C1 subtype, defined by heightened RNASE1 expression; the C2 subtype, distinguished by increased IGFBP3 expression; the C3 subtype, identified by HHATL expression; and the C4 subtype, recognized by GCG expression.