Cutaneous endometriosis in the umbilical region: the usefulness of CD10 in identifying the interstitium of ectopic endometriosis.

Endometriosis is a condition in which endometrium or endometrium-like tissue grows in areas other than the endometrium and is often found within the pelvis such as in the uterus or ovary, but occasionally develops ectopically in the skin. In this paper, we report a case of cutaneous endometriosis in the umbilical region found in a 37-year-old woman with no history of pregnancy. The lesion was a brown, firm and elastic nodule, 9 mm x 7 mm in size, and caused bleeding as well as pain which increased during menstruation. Histopathological findings revealed that there were small and large glandular cavity structures in the dermis and the edematous interstitium around it. On immunohistochemical staining for estrogen and progesterone receptors, the cellular nuclei of glandular cavity walls were mainly found to be positive for both, and cells in the edematous interstitium around the glandular cavity were positive for CD10. Consequently, we diagnosed this case as cutaneous endometriosis in the umbilical region. CD10 was initially described as a tumor-specific antigen found in acute lymphoblastic leukemia. Recently, the usefulness of CD10 in diagnosing endometriosis in addition to various types of lymphoma or blood cancer has been confirmed, and in our case it also proved to be as useful as estrogen receptor or progesterone receptor in the definitive diagnosis of endometriosis.