CD10 is useful in demonstrating endometrial stroma at ectopic sites and in confirming a diagnosis of endometriosis

We read with interest the article by Sumathi and McCluggage entitled “CD10 is useful in demonstrating endometrial stroma at ectopic sites and in confirming a diagnosis of endometriosis” in a recent issue of this journal.¹ Coincidentallay, we did the same kind of study regarding CD10 for our intradepartmental research work. Regarding cases of endometriosis of the ovary, we also included cases that were “suggestive of endometriosis”, which is described in Ackerman’s surgical pathology.² It reads: “Not frequently, the repeated hemorrhages have totally destroyed the endometrial tissue, the cyst being lined by several layers of hemosiderin-laden macrophages. Under these circumstances, the most the pathologist can do is to report the case as a hemorrhagic cyst and comment that the changes are ‘consistent’ with those of endometriosis.” The term “presumptive endometriosis” is also used in Blaustein’s pathology of female genital tract.³ Our cases that were suggestive of endometriosis showed positive cytoplasmic staining of CD10 in their stromal component, and were in agreement with the description in Ackerman’s surgical pathology. Thus, by using CD10 immunostaining, we can make a definite diagnosis of ovarian endometrial cyst even if there is no obvious component of endometrial epithelium. We also had an interesting case of diaphragmatic endometriosis in a patient with catamenial pneumothorax,⁴ in addition to a very rare case of intraluminal endometriosis of the fallopian tube occluding the tubal lumen.³ In these cases, CD10 was also useful to confirm the diagnosis because glandular components were noted within the muscle of the diaphragm and in the muscle layer of the fallopian tube, mimicking invasive adenocarcinoma with lymphoid stroma. Sumathi and McCluggage described three cases that were negative for CD10 in their study. I wonder if they found cilia in those glands in these cases, and if they changed their diagnosis of endometriosis because of the negativity of CD10. Some cases of endometrial polyp are clinically misdiagnosed as “cervical polyp” and these cases can correctly be diagnosed by using CD10 immunostaining. CD10 was useful in our study for the confirmation of such cases. In addition, we incidentally found that some endocervical looking glands situated within the lamina propria of the uterine cervix were surrounded by CD10 positive stromal cells, which could be indicative of superficial endometriosis of the uterine cervix. However, the diagnosis can be missed by haematoxylin and eosin staining alone because the stromal component is too sparse or loose for the endometrial stroma.³ Finally, we would like to add some more information regarding CD10 in the field of gynaecological pathology. It is of note that mesonephric remnants and tumours are positive for CD10.^5,6 Because there have been no good markers to identify mesonephric remnants and mesonephric derived tumours, the use of CD10 can be valuable in such instances.