Parity and NIS Expression in Atypical Cells of Triple-Negative Breast Cancer, and Prognosis

Breast cancer is one of the most common malignancies worldwide, affecting 2.3 million and causing 670,000 deaths in women annually. However, data indicate that the risk of developing breast cancer decreases with pregnancy at a young age, and each subsequent pregnancy further reduces the risk by approximately 10%. One of the characteristics inherent in both the mammary gland epithelium in pregnant women and luminal epithelial adenocarcinomas is the increased expression of NIS—the sodium/iodide symporter, whose defective cytoplasmic forms possess pro-oncogenic properties. Therefore, the analysis of the degree of influence of pregnancy on NIS expression in breast cancer cells is of medical interest. The aim of this study is to conduct a comparative morphological analysis of NIS expression in breast cancer cells according to the number of pregnancies of each patient. This study included 161 patients with triple-negative breast cancer who visited the P.A. Herzen Moscow Oncology Research Institute from 2020 to 2023. Immunohistochemical examination was performed using antibodies to NIS. The gravidity status of women was determined based on provided medical documentation. The degree of NIS expression was assessed using a modified Gainor scale. Statistical analysis was performed using mean and standard deviation (SD) depending on the normality of the distribution (Lilliefors test: p > 0.20); a p-value ≤ 0.05 was considered statistically significant. The degree of correlation between variables was assessed using Kendall’s tau rank correlation coefficient. A weak to moderate negative correlation (τ: −0.369) was found between the number of pregnancies and the degree of NIS expression in triple-negative breast cancer cells. In patients with triple-negative breast cancer, a weak to moderate negative correlation was found between the degree of NIS expression and gravidity status. The discovered phenomenon is likely due to the terminal differentiation of the mammary gland epithelium that occurs during pregnancy. This may potentially indicate the suppression of pro-oncogenic properties of atypical cells developed from the epithelium that has undergone terminal differentiation. © 2025 by the authors.