**1. Introduction**

Breast cancer is the most frequent disease among women, according to the World Health Organisation (WHO), and it is the second leading cause of death from cancer, after lung cancer. It is considered a severe health concern that affects patients' quality of life as well as their psychological well-being, It is the main cause of death among women aged 45 to 55 years old. The incidence of breast cancer is expected to grow by 85 per 100.000 women by 2021 [1]. Experts estimate that by 2050, there will be approximately 3.2 million new BC cases each year worldwide,

based on population increase. Although there is no single risk factor for the majority of breast cancer patients, there are a number of well-known risk factors, including obesity, lack of physical activity, consumption of alcohol, hormone replacement therapy, increased breast density, and inherited genetic susceptibility due to mutations in autosomal dominant genes, which contribute for 5–10% of all breast cancer cases in the United States [2]. Treatment for BC is difficult since it is a heterogeneous illness with various subtypes that have different but distinct clinical and biochemical characteristics. As a result, identifying BC subtypes is critical for determining the optimal treatment approach [3]. Breast cancer may be in situ or invasive, with in situ tumours being the easiest to cure. Invasive breast cancers, especially invasive ductal carcinoma (which accounts for 80% of all invasive breast cancers), are a major source of concern. While receptor-specific therapy is used to treat the first two types of breast cancer, chemotherapy remains the mainstay of TNBC treatment [4]. BC is characterised as basal-like or non-basal-like according on the cell type of origin (luminal or basal/myoepithelial cell compartment). The aforementioned, also referred to as "triple-negative," contributes approximately 10% of all BCs. Understanding the etiological heterogeneity of BC subgroups will aid in directing therapy, predicting survival, and impacting preventive measures due to the complexity of biology [5]. With the standardisation of systemic chemotherapy as the gold-standard method for most cancer types and the moderate increase in both survival rates and toxicity reduction, targeted therapy has undoubtedly garnered the greatest scholarly attention and financing from the pharmaceutical sector. Nonetheless, resistance to treatment is the "major" issue, and a significant increase in survival rates is still a pipe dream for researchers. It is important to note that tremendous progress has been achieved in the area of breast cancer research during the last decade. The 'battle' against this mysterious and aggressive form of cancer, however, is still ongoing [6]. The purpose of this review article is to provide a broad overview of the molecular basis of drug resistance in breast cancer, as well as a detailed assessment of current treatment options and potential new treatment methods for drug-resistant breast cancer. Finally, we go through present problems and future prospects in drug-resistant breast cancer therapy.
