In an in vivo xenograft model, inhibition of the ERK protein by Silibinin, administered at IC50 (the concentration required to achieve 50% inhibition) and 2 × IC50 (twice the concentration required to achieve 50% inhibition) for 48 h, triggered a reduction in the mitochondrial membrane potential and subsequent Cyt-c release, ultimately driving apoptosis in PC cells. The gene discussed is MAPK1; the disease is pachyonychia congenita.