Recently, a retrospective study of 928 BC cases revealed that MPO-positive neutrophils (defined as ≥5 cells/tissue punch) were found in 16% of evaluable cases, while the luminal (ER/PR+ and Her2-), Her2-enriched and triple-negative types had positive rates of 13, 29.7, and 26.4%, respectively, in addition, in univariate analyses, infiltration by MPO-positive neutrophils was a significant independent favorable indicator for both OS and DFS. The gene discussed is MPO; the disease is breast cancer.