RSCRR LIBRARY: A Rare Clinical Case of Luminal Subtype A Breast Cancer with Multiple Metastases in a Young Patient

Breast cancer (BC) is a malignant tumor originating in the epithelium of the mammary gland tissue. This pathology ranks second among all oncological diseases and first in terms of incidence among women. In Russia, about 82,000 new cases of BC were detected in 2023, about half of which were luminal A subtype. It is traditionally believed that this subtype is less aggressive, responds well to endocrine therapy, rarely metastasizes, and is virtually unresponsive to chemotherapy due to its low aggressiveness. In this article, we describe a clinical case of luminal A subtype breast cancer, which was characterized by distant metastases (M1) and multiple regional metastases (N3c) with a small primary tumor size (T1b). In addition, the patient responded well to chemotherapy, which is unusual for this subtype due to its low proliferative activity. This clinical case illustrates the possibility of rapid lymphogenous spread and a good response to chemotherapy in luminal A subtype breast cancer, despite a low proliferative activity index (Ki-67<20%) and low malignancy of cells, indicating the possibility of using different approaches to the treatment of metastatic breast cancer of this subtype. This makes it possible to develop new treatment regimens for women with metastatic breast cancer.