Genetic Testing of Breast Cancer Patients with Very Early-Onset Breast Cancer (≤30 Years) Yields a High Rate of Germline Pathogenic Variants, Mainly in the BRCA1, TP53, and BRCA2 Genes.

Simple Summary: Identification of germline pathogenic variants in breast cancer patients holds significant importance for accurate risk assessment and therapeutic interventions. However, research focusing on very young breast cancer patients remains limited. Our objective was to describe the prevalence, gene, and variant spectra alongside clinicopathological characteristics and outcomes of women diagnosed with breast cancer ≤30 years. Our observations revealed that one in three patients carried predisposing variants distributed in eight established breast cancer genes. Predominantly, causative variants implicated loss-of-function of BRCA1, TP53, and BRCA2, with TP53 emerging as the second most frequently mutated gene within this cohort. While carrier status did not impact event-free survival, carriers who underwent neoadjuvant chemotherapy exhibited improved prognostic outcomes. Our data underscore the substantial proportion of patients with hereditary predisposition, advocate for the inclusion of TP53 genetic testing, and suggest possible benefits of neoadjuvant chemotherapy in this very young group of breast cancer patients. Early-onset breast cancer constitutes a major criterion for genetic testing referral. Nevertheless, studies focusing on breast cancer patients (≤30 years) are limited. We investigated the contribution and spectrum of known breast-cancer-associated genes in 267 Greek women with breast cancer ≤30 years while monitoring their clinicopathological characteristics and outcomes. In this cohort, a significant proportion (39.7%) carried germline pathogenic variants (PVs) distributed in 8 genes. The majority, namely 36.7%, involved BRCA1, TP53, and BRCA2. PVs in BRCA1 were the most prevalent (28.1%), followed by TP53 (4.5%) and BRCA2 (4.1%) PVs. The contribution of PVs in CHEK2, ATM, PALB2, PTEN, and RAD51C was limited to 3%. In the patient group ≤26 years, TP53 PVs were significantly higher compared to the group 26–30 years (p = 0.0023). A total of 74.8% of TP53 carriers did not report a family history of cancer. Carriers of PVs receiving neoadjuvant chemotherapy showed an improved event-free survival (p < 0.0001) compared to non-carriers. Overall, many women with early-onset breast cancer carry clinically actionable variants, mainly in the BRCA1/2 and TP53 genes. The inclusion of timely testing of TP53 in these patients provides essential information for appropriate clinical management. This is important for countries where reimbursement involves the cost of genetic analysis of BRCA1/2 only. [ABSTRACT FROM AUTHOR]