ARIAS STELLA CHANGES/REACTION. The diagnosis in this case is straightforward and relatively easy in this very young patient with a positive pregnancy test. However, it can be challenging in an older patient who comes in with bleeding. Arias Stella reaction shows endometrial glands lined by clear cells with atypia. Intranuclear inclusions (arrow) are often present. There can be occasional mitotic activity, which can further heighten its mimicry to clear cell carcinoma. Furthermore, the clear cells of Arias Stella are positive for Napsin and HNF1Beta, markers that are positive in clear cell carcinoma. AMACR is reportedly negative in Arias Stella while being positive in clear cell carcinoma although too few cases are tested to be confident of this claim.
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