Systemic therapy-induced resistance and toxicity in breast cancer: Sensitization and mitigation strategies

Breast cancer is the most frequently reported cancer in women, with high mortality and morbidity globally. Paclitaxel, doxorubicin, tamoxifen, cisplatin, and 5-fluorouracil are cornerstones of standard-of-care treatment for primary and advanced breast cancers, targeting distinct molecular mechanisms. However, the evolution of acquired resistance primarily leads to treatment failure and progression to metastasis, ultimately to patient mortality. Furthermore, their effectiveness is limited by potential toxicities in various organs. These limitations present an extreme challenge for the management of breast cancer at the advanced stage. This review uncovers recent updates on acquired resistance mechanisms toward standard-of-care treatments driven by deeply rooted heterogeneity and aggressive nature through direct counteracting of its core action, hyperactivation of survival pathways, silencing of core cell death pathways, derepressing the expression of multidrug resistance proteins, metabolic reprogramming, epigenetic modifications, and exosome-mediated horizontal transfer of resistance phenotype. In addition, we discuss recent updates on potential strategies to overcome resistance and toxicities induced by standard-of-care treatments. Ultimately, this review helps to identify novel strategies targeting pathways to reverse resistance and reduce toxicity in breast cancer patients.