Hereditary breast cancer beyond BRCA: clinicopathological characteristics and long-term outcomes.

Limited data exist on hereditary breast cancer characteristics and treatment driven by germline mutations beyond BRCA. Our primary aim is to describe the tumour and patient characteristics, treatment patterns and outcomes in patients with non-BRCA hereditary breast cancer with a focus on CHEK2, ATM, PALB2 and TP53 variants. This is a retrospective single centre hospital-based cohort study of adult patients with a known (likely) pathogenic germline mutation and breast cancer diagnosis in UZ Leuven before April 2022. Data collection included baseline demographics, breast cancer characteristics, treatment patterns and disease outcome variables. Cohorts of patients with variants in different genes will be compared. We retrieved 185 patients with variants in ATM (N = 40), CHEK2 (N = 114), PALB2 (N = 8) and TP53 (N = 23). Median age was significantly lower in the TP53 group (36 years, p = 0.001). Only estrogen receptor (ER) status (p = 0.005) and breast cancer subtype (p < 0.001) differed significantly across the defined gene cohorts. HER2-positive disease was more frequent in the TP53 subgroup (59.1%, p < 0.001). Neoadjuvant chemotherapy was more commonly administered in the PALB2 and TP53 cohorts (p = 0.011). Univariate and multivariate survival analysis by gene cohort showed no significant difference in survival outcomes. In our series, we confirm that TP53 carriers are younger at breast cancer diagnosis and have more often HER2-positive breast cancer. Triple-negative breast cancer is more frequent in the PALB2 carriers, while ER-positivity is most common in ATM and CHEK2 carriers. Survival outcomes were similar across different gene cohorts in this study.