SATB2 is Consistently Expressed in Squamous Morules Associated With Endometrioid Proliferative Lesions and in the Stroma of Atypical Polypoid Adenomyoma.

So-called squamous morules are closely associated with endometrioid proliferative lesions, in the endometrium and the ovary. Morules have an unusual immunophenoptype, typically exhibiting nuclear staining with β-catenin, positivity with CDX2, CD10, and p16 and are negative with hormone receptors and p63. We report the previously undescribed occurrence of consistent SATB2 nuclear positivity within morules. Nuclear positivity was present in 38/43 (88%) cases of morules (24 focal; 14 diffuse) while all cases of nonmorular squamous metaplasia in endometrioid proliferative lesions (n=13) were SATB2 negative, except for occasional positive nuclei in 1 case. We also observed that the stromal cells of atypical polypoid adenomyoma typically exhibited diffuse nuclear immunoreactivity with SATB2 while the stromal cells of other endometrial polypoid lesions (endometrial polyp, adenomyoma, adenosarcoma) were usually negative, although there was focal weak staining in occasional cases. Pathologists should be aware of this previously undescribed phenomenon which represents a further example of the unusual immunophenotype of so-called squamous morules. The reasons underlying SATB2 nuclear positivity in squamous morules and the stroma of atypical polypoid adenomyoma are unknown.