Metachronous bilateral disease was most commonly found in CHEK2 mutation carriers with 5/16 (31%) developing subsequent contralateral disease after a diagnosis of unilateral DCIS (in two, this was in the form of an invasive disease, in two LCIS and in one DCIS) compared to 2/22 (9%) for BRCA2. The latter, however, will be influenced by the fact that nine of the BRCA2 carriers elected for bilateral prophylactic mastectomies based on their family history or the results of genetic testing (five underwent genetic testing). The gene discussed is BRCA2; the disease is ductal breast carcinoma in situ.