Distinct biological and molecular characteristics of breast cancer in young women: a narrative review

Breast cancer in young women (defined as ≤40 years of age) presents unique clinical and biological challenges. While it accounts for a small proportion of total breast cancer cases, it is often associated with more aggressive tumor phenotypes, higher-grade histology, and advanced-stage diagnosis. Young patients are more likely to develop triple-negative and HER2-positive subtypes, which are linked to poor prognostic outcomes and limited treatment options. These clinical patterns suggest that age-specific molecular mechanisms drive tumor behavior in this population. Emerging molecular profiling studies have revealed distinct genomic, transcriptomic, and epigenetic features in breast cancer arising in young women. Mutations in TP53, BRCA1/2, and other DNA repair genes are more prevalent, along with basal-like intrinsic subtypes that exhibit high proliferation and genomic instability. The tumor microenvironment also demonstrates unique immune signatures, including increased tumor-infiltrating lymphocytes and inflammatory cytokine expression, which may influence response to immunotherapy and tumor progression. This review synthesizes current knowledge on the unique tumor biology of breast cancer in young women, highlighting the need for precision oncology approaches that account for age-related tumor behavior. Enhanced characterization of this population may ultimately improve survival outcomes and quality of life for young women affected by breast cancer.