ESR1 and cytomegalovirus infection: To examine whether the grade of HCMV infection was associated with known relevant clinical factors for breast cancer, such as SLN status, Estrogen Receptor alpha (ERα), Progesterone receptor (PR) and Elston grading (Her2-neu was only available for a small number of patients), we estimated the number of HCMV IE- and LA-positive cells using a four-grade scale.