HORMA domain-containing protein 1 (HORMAD1) is a protein that promotes meiotic recombination and its expression is usually restricted to germ-line cells, although it has been shown to be actively expressed out of context in about 60% of triple-negative breast cancers (TNBCs). A team at The Institute of Cancer Research has found that this aberrant expression in tumor cells perturbs mitotic arrest and generates aneuploidy, leading to a weakening of the spindle assembly checkpoint and in kinetochore-microtubule error correction.