Introduction The current work is based on the medical case of a 63-year-old patient without the previous medical history of breast cancer who was diagnosed with invasive ductal carcinoma. With the help of immunocytochemical methods, it was found that the tumour mass is oestrogen receptor-positive, progesterone receptor-positive and HER2 negative. After lumpectomy, the woman underwent chemotherapy, however, during this period, she suffered from bladder infections that required additional antibiotic therapy. The purpose of this essay is to investigate the pathophysiology of hormone receptor-positive breast cancer, the molecular basis of the therapeutic agents’ activities, their potential side effects and enterococcal virulence factors that provoke bladder infections. Pathophysiology of Hormone Receptor-Positive Breast Cancer The examination of physiological processes that result or associated with certain disease or injury is highly essential both for theoretical research concerning this medical condition and the definition of treatment methods. The contemporary understanding of the etiopathogenesis of breast cancer addresses the origin of invasive cancer through a substantive number of molecular alterations at the cellular level (Chalasani, 2019). The result of these alterations is breast epithelial cells that possess immortal features and are characterized by uncontrolled growth. Genomic profiling has already demonstrated the existence of several discrete subtypes of breast tumour with distinct clinical behaviour and natural histories. The precise number of molecular alterations and cancer subtypes remains to be completely elucidated (Chalasani, 2019). In general, subtypes are characterized by the absence or presence of oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) (Chalasani, 2019). This differentiation provided the perception of breast cancer “not as a set of stochastic molecular events” but a limited range of separable disorders of distinct cellular and molecular origins (Chalasani, 2019, para. 3). Moreover, this approach has changed the understanding of breast cancer aetiology, its prevention and risk factors that appear according to the disease’s subtype. This view has substantially influenced breast cancer research and the strategies of treatment as well. Every breast cancer subtype has distinct epigenetic and genetic aberration. According to The Cancer Genome Atlas Network, there are four main tumour subtypes – luminal A, luminal B, basal-like and HER2-positive breast cancer (Chalasani, 2019). HER2-positive cancer is characterized by the presence of HER2 and the absence of ER (Chalasani, 2019). It is insignificantly common though highly aggressive breast cancer subtype with high grade histology (Chalasani, 2019). This subtype presents a potential threat for African American ethnicity and women at a relatively young age. Basal-like breast cancer is an aggressive subtype with high mitotic rate and histology that is defined by the absence of ER, PR and HER2 (Chalasani, 2019). It is substantively virulent for premenopausal African American and young women as well. Luminal A and luminal B subtypes are generally similar; the main difference between them is the presence of HER2 in luminal B subtype and its absence in luminal A breast cancer (Chalasani, 2019). Invasive ductal carcinoma that 63-y