Expression of the Cystatin SN (CST1) in Breast Cancer and Its Association With Clinical Characteristics: A Cross-Sectional Study.

Background Breast cancer is a major global health concern with increasing incidence and mortality, particularly in low- and middle-income countries such as Bangladesh. Cystatin SN (CST1) has emerged as a potential oncogenic biomarker; however, its expression and clinical relevance remain underexplored in Bangladeshi populations. This study aimed to evaluate CST1 expression in tumor and adjacent normal breast tissues and to assess its association with the clinical characteristics of breast cancer patients. Methods A hospital-based cross-sectional study was conducted at Dhaka Medical College, Bangladesh, from January 2023 to June 2023. A total of 34 adult female patients (aged 25-70 years) with histologically confirmed, treatment-naïve breast cancer were recruited via purposive sampling. Paired tumor and adjacent normal tissue samples were collected following a modified radical mastectomy. CST1 gene expression was measured via next-generation sequencing. The data were analyzed via SPSS version 26 (IBM Corp., Armonk, NY, USA). The Wilcoxon signed-rank test was used to compare gene expression between paired samples, and Spearman's correlation coefficient was applied to assess associations with clinical variables. Results The mean age of the participants was 47.41 ± 12.19 years. CST1 gene expression was significantly greater in tumor tissue than in adjacent normal tissue (median -0.068 vs -1.988, p = 0.035). A statistically significant positive association was observed between CST1 expression and a family history of breast cancer (rho = 0.267, p = 0.027). In contrast, CST1 expression was significantly negatively associated with contraceptive use (rho = -0.437, p < 0.001) and weakly negatively associated with breastfeeding history (rho = -0.240, p = 0.049). No significant associations were observed between CST1 expression and age, body mass index, parity, or age at menarche. Conclusion CST1 gene expression is significantly elevated in tumor tissue and is associated with selected clinical factors, suggesting its potential relevance as a molecular marker in breast cancer. Further large-scale and longitudinal studies are needed to establish its clinical and prognostic significance.