However, both traditional hematoxylin and eosin (H&E) staining and immunohistochemical staining for CD138 (syndecan-1), a sensitive marker for plasma cells, have limitations in diagnosing CE, including dependence on endometrial samples, variability in staining, observer subjectivity, inconsistent timing of sample collection during the menstrual cycle, and unclear clinical significance of minimal plasma cell infiltration (18, 19). This evidence concerns the gene SDC1 and cholesteryl ester measurement.