Assessment of Human Epididymis Protein 4 Expression in Breast Ductal Carcinoma In Situ

<b>Background/Objectives</b>: Elevated expression of human epididymis protein 4 (HE4) has been observed in breast cancer and is associated with cancer progression; however, its role in ductal carcinoma in situ (DCIS) remains unclear. This study aimed to evaluate HE4 levels in serum and tissue from patients with DCIS and their correlation with clinicopathological features. <b>Methods</b>: Preoperative serum HE4 levels were measured in 59 DCIS patients. HE4 mRNA and protein expression in DCIS and adjacent normal tissues were assessed using RNAscope in situ hybridization and immunohistochemistry, respectively. An additional independent tissue microarray of 41 DCIS cases was also analyzed for HE4 expression in tumor tissue only. Furthermore, the BreastMark database was applied to assess the prognostic significance of HE4 expression in a larger cohort of breast cancer. <b>Results</b>: Serum HE4 levels (mean ± SD: 39.4 ± 11.9 pmol/L) were within the normal range and showed no significant correlation with clinicopathological parameters except menopausal status. HE4 expression was significantly higher in DCIS tissues compared to adjacent normal tissues, with a positive correlation between mRNA and protein levels (<i>r</i> = 0.771, <i>p</i> < 0.001). High HE4 mRNA and protein expression was associated with ER positivity, HER2 negativity, low stromal tumor-infiltrating lymphocyte density, and HR+/HER2- subtypes, but was not predictive of DCIS recurrence. In breast cancer patients, high HE4 expression was significantly correlated with improved survival outcomes. <b>Conclusions</b>: Although serum HE4 is not elevated in DCIS, high HE4 expression in tissue is associated with favorable clinicopathological features. These findings highlight the need for further investigation into the potential prognostic role of HE4.