Immunohistochemical analysis showed diffuse positivity for SMA, Desmin, and HMB-45, weak-to-moderate nuclear staining for TFE3, and a Ki-67 proliferation index of less than 1%, supporting the diagnosis of micronodular PEComa of the appendix. The gene discussed is PMEL; the disease is neoplasm with perivascular epithelioid cell differentiation.