Figure 3:

Mixed gastrointestinal-type mucinous and endometrioid borderline tumor associated with endometriosis (MO-2). (A-D) Sections, illustrating (A) endometrioid component; (B) mucinous component; (C) admixture of endometrioid and mucinous glands, with neutral mucin exclusive to the mucinous glands (inset, AB/PAS histochemical stain); (D) adjacent endometriosis, with corresponding ARID1A immunohistochemistry (E), showing loss of expression exclusive to neoplastic glands. (F) Sequencing reads of the ARID1A locus, showing a frameshift mutation, due to small deletion, present in endometriosis, with loss-of-heterozygosity in tumor (endometrioid component shown).