PurposeThe human endometrium consists of different layers (basalis and functionalis) and undergoes different phases throughout the menstrual cycle. In a former paper, our research group was able to describe MSX1 as a positive prognosticator in endometrial carcinomas. The aim of this study was to examine the MSX1 expression in healthy endometrial tissue throughout the different phases to gain more insight on the mechanics of MSX-regulation in the female reproductive system.Materials and methodsIn this retrospective study, we investigated a total of 17 normal endometrial tissues (six during proliferative phase and five during early and six during late secretory phase). We used immunohistochemical staining and an immunoreactive score (IRS) to evaluate MSX1 expression. We also investigated correlations with other proteins, that have already been examined in our research group using the same patient collective.ResultsMSX1 is expressed in glandular cells during the proliferative phase and downregulated at early and late secretory phase (p= 0.011). Also, a positive correlation between MSX1 and the progesterone-receptor A (PR-A) (correlation coefficient (cc) = 0.0671;p= 0.024), and the progesterone receptor B (PR-B) (cc = 0.0691;p= 0.018) was found. A trend towards negative correlation was recognized between MSX1 and Inhibin Beta-C-expression in glandular cells (cc = − 0.583;p-value = 0.060).ConclusionMSX1 is known as a member of the muscle segment homeobox gene family. MSX1 is a p53-interacting protein and overexpression of homeobox MSX1 induced apoptosis of cancer cells. Here we show that MSX1 is expressed especially in the proliferative phase of glandular epithelial tissue of the normal endometrium. The found positive correlation between MSX1 and progesterone receptors A and B confirms the results of a previous study on cancer tissue by our research group. Because MSX1 is known to be downregulated by progesterone, the found correlation of MSX1 and both PR-A and -B may represent a direct regulation of the MSX1 gene by a PR-response element. Here further investigation would be of interest.