CD44s expression is reduced in endometriotic lesions compared to eutopic endometrium in women with endometriosis.

Immunohistochemical expression of the standard form of CD44 (CD44s) was examined in archival formalin-fixed endometriotic and matching eutopic endometrial tissue obtained from 25 patients in proliferative (N = 16) and secretory (N = 9) stages of the cycle. CD44s was expressed in most eutopic endometria and endometriotic tissue. Its expression was significantly higher in secretory than in proliferative phase endometrium. It was low but detectable in 13 of 16 proliferative phase biopsies. The majority of these endometria exhibited both glandular and stromal staining (63%). In the secretory phase, glandular cells exhibited a significantly greater intensity of staining compared to stromal cells. In endometriotic tissue, stromal cell CD44s expression did not differ between tissue types in either stage of the cycle. In contrast, glandular expression in endometriotic tissue during the secretory phase was reduced (p < 0.05) compared to eutopic endometrium. It was absent in 66% of cases and reduced in the remaining cases. Our results indicate a correlation between CD44s expression and secretory differentiation of endometrial glands in the cycle, suggesting hormonal regulation of its expression. This cyclic pattern of CD44s expression was lost in corresponding endometriotic tissue. Reduced expression of CD44s in endometriotic tissue may provide insight into the pathophysiology of endometriosis.