Table 5.

The most useful histopathologic and molecular genetic features for the diagnosis of uterine corpus mesonephric-like adenocarcinomas.

Morphological features	(1) In combination of a variety of growth patterns including tubular, glandular, papillary, retiform, glomeruloid, sex-cord like, spindle cells, and solid; (2) Columnar to cuboidal cells with distinctive nuclear features resembling those seen in papillary thyroid carcinoma, such as nuclear grooves, nuclear overlap, and open chromatin; (3) The presence, at least focally, of densely eosinophilic intraluminal secretions in the tubules; (4) The lack of marked nuclear atypia and pleomorphism, and unequivocal squamous differentiation.
Immunohistochemical features	(1) Mostly positive for GATA3 and TTF1, and less commonly for calretinin and luminal CD10; (2) Patchy P16 and “wild type” P53 expression; (3) Negative for estrogen receptor (can be focally positive) and progesterone receptor.
Molecular genetic features	Somatic KRAS mutations (in up to 90% cases), with or without mutations in PIK3CA, PTEN, and CTNNB1.