The authors have studied, analyzed, and summarized the data from publications of recent decades regarding the effect of vitamin D on the outcomes of breast cancer treatment, the place and role of its active form and metabolites at the stages of carcinogenesis, in vivo and in vitro manifestations of its “non-classical” effects, prediction of the possible practical application of the results obtained at the molecular-cellular level. Studying the potential influence of vitamin D on the effectiveness of systemic therapy for breast cancer occupies an important place in modern research. The connection between vitamin D deficiency and breast cancer is a field of extensive debate that continues on many aspects (risk factors, predictors, treatment effectiveness, survival). In this literature review, which included studies different in design and sampling, we attempted to systematize the results obtained in recent years on this topic and to evaluate their potential implementation in clinical practice. Particularly noteworthy are scientific works of various designs devoted to identifying the potential predictive influence of initial and final vitamin D levels on the success of neoadjuvant treatment and enhancement of tumor response in patients with locally advanced breast cancer. The systematized data obtained serve as a vector for further scientific research among patients with breast cancer in Ukraine.