Patients were subdivided into different comparison groups based on tumor characteristics, including grade (Grade 1-3), stage (Stages 1, 2, 3 and 4) at the first breast cancer diagnosis, subtype (ER or PR+/Her2-ve, ER or PR+/Her2+ ve, ER- and PR-/Her2-ve, triple-negative), Ki67 staining grade (high, low), histology (invasive lobular carcinoma, invasive ductal carcinoma, others), presence (NPlus) or absence (N0) of lymph node involvement and race (Caucasian, African-American). This evidence concerns the gene MKI67 and breast cancer.