CYP4B1 Expression in Breast Cancer: An Immunohistochemical Study with Complementary in silico Analyses.

Purpose: Cytochrome 4B1 (CYP4B1) is a monooxygenase extrahepatic enzyme, recently found expressed in several malignancies. However, the role of CYP4B1 in breast cancer is still undetermined. Patients and Methods: The study consisted of two complementary components. First, CYP4B1 protein expression was evaluated by immunohistochemistry using a breast cancer tissue microarray (n = 207 tumors; n = 8 normal breast tissues). Second, in silico analyses were performed using publicly available databases and included transcriptomic expression profiling, survival analysis, protein-protein interaction analysis (PPI), functional enrichment analysis, drug-sensitivity correlations, and AlphaFold-based structural assessment. Results: Immunohistochemical analysis demonstrated focal and heterogeneous CYP4B1 protein expression, which was detected in 18.3% of breast tumors and was significantly associated with lower histological grade. No CYP4B1 immunoreactivity was observed in the sampled normal breast tissues under the experimental conditions. In silico analyses demonstrated reduced CYP4B1 mRNA expression in breast cancer at the population level, compared with normal breast tissue. Survival analysis showed no statistically significant differences between CYP4B1 expression groups. According to PPI analysis, CYP4B1 is part of a closely related redox-regulatory and xenobiotic-metabolizing module enriched in CYPs, GSTs, and SULTs. Structural analysis provided contextual support for the previously reported association of the P427S meander-region substitution with reduced catalytic competence. Weak exploratory correlations were observed between CYP4B1 expression and drug sensitivity metrics; however, these findings were descriptive and did not indicate clinically meaningful resistance. Conclusion: Immunohistochemical analysis demonstrated that CYP4B1 protein expression is focal and heterogeneous, being retained in only a small subset of breast tumors and associated with lower histological grade. Bioinformatics analyses showed reduced CYP4B1 mRNA expression in breast cancer and identified CYP4B1 within xenobiotic metabolism and redox-regulatory networks. Collectively, these findings provide a descriptive multilevel characterization of CYP4B1 in breast cancer; however, its prognostic and therapeutic significance remains exploratory and requires further functional validation.