In pure DCIS, numerous clinicopathological parameters indicating poor DCIS prognosis were associated with high IDH2 expression (Table 1) including younger age at diagnosis, (p = 0.035), larger tumour size, higher nuclear grade (both p < 0.0001), presence of comedo type necrosis (p = 0.001), hormonal receptor negativity and HER2 positivity (all p < 0.0001). The gene discussed is IDH2; the disease is ductal breast carcinoma in situ.