This study aimed to evaluate a series of ER-negative tumours from a large consecutive cohort of older women with early operable primary breast cancer, regardless of their initial primary treatment, by analysing (1) their long-term clinical outcome; and (2) their biological features in terms of progesterone receptor (PgR), human epidermal receptor (HER) 2 and Ki67. The gene discussed is MKI67; the disease is breast cancer.