Comparative analysis of mutational patterns in triple negative breast cancer before and after neoadjuvant chemotherapy in patients with residual disease

•TNBC remains a heterogeneous and challenging subset of breast cancer.•The mutational landscape in TNBC patients with residual disease remains stable pre- and post-NAC, with no recurrent variants evident.•Post-NAC samples showed a significant increase in AR gene variants, suggesting potential prognostic/predictive implications. Triple-negative breast cancer (TNBC) is a heterogeneous disease with poor survival compared to other subtypes. Patients with residual disease after neoadjuvant chemotherapy (NAC) face an increased risk of relapse and death. We aimed to characterize the mutational landscape of this subset to offer insights into relapse pathogenesis and potential therapeutic targets. We retrospectively analyzed archived paired (pre- and post-NAC) tumor samples from 25 patients with TNBC with residual disease using a targeted 72-gene next-generation sequencing panel. Our findings revealed a stable mutational burden in both pre- and post-NAC samples, with a median count of 12 variants (IQR 7–17.25) per sample. TP53, PMS2, PTEN, ERBB2, and NOTCH1 variants were observed in pre-NAC samples predominantly. Notably, post-NAC samples exhibited a significant increase in AR gene mutations, suggesting potential prognostic and predictive implications. No difference in mutational burden was found between patients who did and did not receive platinum (p = 0.94), or between those with and without recurrence (p = 0.49). We employed K-means clustering to categorize the patients based on their variant profiles, aiding in the prediction of possible patterns associated with recurrence. Our study was limited by its small sample size and retrospective design, suggesting the need for further validation in larger prospective cohorts.