Gastrointestinal-type mucinous borderline tumor with intraepithelial carcinoma of Mullerian-type (MO-3). (A) Low-magnification image showing both components; (B) area morphologically suggestive of endometriosis, supported by CD10 immunoreactivity in stromal cells (C), which is contiguous with a focus with marked nuclear atypia and cytoplasmic clearing (D). (E) Another area of mucinous borderline tumor, exhibiting goblet cells. Immunohistochemical stains for (F) ER and (G) CDX2, shows differential expression in morphologically distinct areas, in line with mixed Mullerian and gastrointestinal-type mucinous differentiation.