ABSTRACT
Young-onset breast cancer (YOBC) is defined as breast cancer (BC) diagnosed in women under the age of 40 years. 1 YOBC accounts for 5% of all female BCs and is associated with higher stage disease on presentation, higher rates of local recurrence and distant disease and poor survival. 2 A higher number of YOBC patients carry inherited pathogenic BRCA1 or BRCA2 variants (gBRCA1/2) compared to older patients diagnosed with BC. The BRCA genes are tumour suppressor genes involved in DNA repair by homologous recombination. They have an autosomal dominant pattern of inheritance. 3 Pathogenic mutations in the BRCA genes result in ineffective DNA repair, leading to chromosomal instability. They are characterised by high penetrance, with a lifetime BC risk of up to 70%, and are associated with aggressive histopathological characteristics, such as triple-negative breast cancer (TNBC). 4 However, there is no clear evidence on the impact of gBRCA mutations on the prognosis of patients with BC. The Prospective Study of Outcomes in Sporadic versus Hereditary Breast Cancer (POSH) study investigated the association between gBRCA1/2 pathogenic variants and clinical outcomes in patients with YOBC.
