Immunohistochemical phenotype is associated with metastatic site in breast cancer: a retrospective pathomorphological study of women from the Lower Aral Sea region, Uzbekistan

Background: Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in women worldwide, and the great majority of these deaths are caused by metastatic disease. Whether the immunohistochemical (IHC) phenotype of breast cancer is associated with the anatomical site of metastasis has been characterized mainly in high-income, registry-based populations, while data from ecologically stressed and medically under-served regions such as the Lower Aral Sea basin are lacking. Methods: We retrospectively reviewed 652 women diagnosed with breast cancer at the Khorezm Branch of the Republican Specialized Scientific-Practical Medical Center of Oncology and Radiology (Uzbekistan) between 2020 and 2024, of whom 213 had metastatic disease (306 metastatic foci). Histological type was assessed on hematoxylin-eosin and van Gieson-stained sections; quantitative morphometry was performed in Fiji/ImageJ; and HER2, estrogen receptor (ER), progesterone receptor (PR) and Ki-67 were assessed by IHC. The association between marker expression and metastatic site (liver, lung, lymph node) was tested in 187 foci with adequate tissue using the chi-square test, with significance at p < 0.05. Results: Invasive ductal carcinoma predominated. Metastatic site was significantly associated with the IHC phenotype. Liver metastases showed the highest frequency of HER2 3+ (45.7%), ER-negativity (65.2%), PR-negativity (69.6%) and high proliferation (Ki-67 [&ge;] 60%; 47.8%), whereas lymph-node metastases were more often hormone-receptor-positive (ER+ 58.7%; PR+ 52.4%) with lower HER2 3+ (22.2%); lung metastases were intermediate (all p < 0.05). The combination of HER2 3+ and Ki-67 [&ge;] 60% was associated with multi-organ spread. Morphometry corroborated these patterns: liver lesions had larger atypical cells (up to 132.8 m), a higher nuclear-to-cytoplasmic ratio (0.76 vs 0.51) and more extensive necrosis and microvascularity than lymph-node lesions. A pragmatic 5-criterion morphological score (histological type, Ki-67, HER2, ER/PR status, atypical-cell size) stratified metastatic risk into three tiers. Conclusions: In this regional cohort, the IHC phenotype of breast cancer tracked the anatomical site of metastasis, with an aggressive HER2-driven, hormone-receptor-negative profile concentrated in liver metastases and a hormone-receptor-positive profile in lymph-node metastases. These findings reproduce established organotropism patterns in a previously uncharacterized population and support phenotype-aware, site-specific surveillance together with a low-cost morphological risk score for resource-limited settings.