Compared with non-carriers, PALB2 pathogenic mutation carriers developed breast cancer at a younger age (47.52 years vs. 51.35 years, p = 0.016) and were more likely to have triple-negative (24.1% vs. 13.4%, p = 0.022) or HER2 negative (87.0% vs. 74.2%, p = 0.031) breast cancer and large breast tumors (> 2 cm) at diagnosis (72.2% vs. 57.0%, p = 0.024).
Where possible, relatives of women found to carry PALB2 mutations were genotyped for the family-specific mutation, mutant transcripts were characterised and breast tumours arising in mutation carriers were recalled and reviewed.
Systematic pathology review was conducted on breast tumours from 28 female carriers of PALB2 mutations (non-carriers of other known high-risk mutations, recruited through various resources with varying ascertainment) and on breast tumours from a population-based sample of 828 Australian women diagnosed before the age of 60 years (which included 40 BRCA1 and 18 BRCA2 mutation carriers).
Aberrant promoter hypermethylation of PALB2 is more frequent than the reported level of PALB2 point mutations in breast tumors from BRCA1/2-negative families and is similar to the frequency of BRCA1 hypermethylation in inherited and sporadic breast and ovarian cancers.