Inherited mutations in PALB2 are the most common cause of familial breast cancer after BRCA1 and BRCA2 but it is possible that current clinical genetic testing might be missing some cancer-causing mutations.  For BRCA1 and BRCA2 many of the cancer-causing mutations involve changes in large sections of these genes (called large genomic rearrangements or LGRs) which need special tests to accuracy detect them. For PALB2, it is currently not known how common these LGRs are and therefore these special tests are not routinely performed.  We conducted the largest study to date of PALB2 LGRs in over 10,000 subjects and show that over 10% of mutation in PALB2 are LGRS and are likely not identified in routine testing. Our work provides strong support for PALB2 LGRs tests to be made standard of care in clinical genetic testing.  (By Professor Ian Campbell, https://jmg.bmj.com/content/early/2022/04/07/jmedgenet-2021-108399 )