Immunohistochemical evaluation was performed using antibodies against cell cycle related proteins ER, PR, p53, p21, p63, and Ki-67 in hyperplasia of usual type (HUT) in specimens of aesthetic reduction mammaplasty (ARM), in specimens of mammaplasty contralateral to breast cancer (MCC), and in specimens of invasive mammary carcinomas (IMC) presenting HUT in the adjacent parenchyma. This evidence concerns the gene ESR1 and Merkel cell skin cancer.