Gestational, or pregnancy—associated, breast cancer (GRC) is a disease that is first diagnosed during pregnancy, in the first year after childbirth, or throughout the entire period of breastfeeding. The long duration of treatment and the unfavorable prognosis associated with breast cancer can be explained by delays in diagnosis and treatment, which arise due to low alertness of doctors, as well as due to the difficulty of interpreting the results of assessing the severity of the condition of the mammary glands. The domestic literature on the diagnosis of breast cancer is extremely limited, which is why further coverage of this topic is relevant. The purpose of the review is to analyze the literature data on the diagnosis of breast cancer. The authors conducted a search for scientific publications in the electronic databases PubMed, eLibrary and Google Scholar. The search used keywords and their combinations: "gestational breast cancer", "breast cancer", "breast cancer associated with pregnancy", "pregnancy", "breastfeeding", "lactation", "MRI", "CT", "mammography", "ultrasound", "biopsy", "diagnosis", "gestational breast cancer", "breast cancer", "breast cancer associated with pregnancy", "pregnancy", "breastfeeding", "lactation", "MRI", "CT", "mammography", "ultrasound", "biopsy", "diagnosis". Breast cancer remains a serious challenge for modern medicine. Various methods are used for its diagnosis and treatment, including puncture biopsy, fine needle biopsy and surgical biopsy. Ultrasound examination plays an important role in monitoring the response to neoadjuvant chemotherapy and monitoring the condition of regional lymph nodes. Further imaging studies, such as ultrasound elastography with, contrast-enhanced ultrasound and hybrid PET/MRI techniques, can significantly improve the diagnosis and treatment of breast cancer. The use of non-contrast diffusion MRI in pregnant patients and lactating women is of particular interest for further research in this area.