Then, we investigated ER levels and ER binding activity in regards to skin cancer initiation, promotion and progression stages (represented by C5N, P1, B9, A5 and CarB cell lines) and we emphasized on the in vitro and in vivo effects of ERα-specific targeting in the aggressive characteristics of CarB by S554fs, a dominant negative mutant of ERα (dnERα). The gene discussed is ESR1; the disease is skin cancer.