Arias-Stella reaction

Arias-Stella reaction, also Arias-Stella phenomenon, is a benign change in the endometrium associated with the presence of chorionic tissue.

Arias-Stella reaction is due to progesterone primarily. Cytologically, it looks like a malignancy and, historically, it was diagnosed as endometrial cancer.

Significance
It is significant only because it can be misdiagnosed as a cancer. It may be seen in a completely normal pregnancy.

Diagnosis
It is characterized by nuclear enlargement and may also have any of the following: an irregular nuclear membrane, granular chromatin, centronuclear vacuolization, and pseudonuclear inclusions.

Five subtypes are recognized:
 * 1) Minimal atypia.
 * 2) Early secretory pattern.
 * 3) Secretory or hypersecretory pattern.
 * 4) Regenerative, proliferative or nonsecretory pattern.
 * 5) Monstrous cell pattern.

History
It was first described by Javier Arias Stella, a Peruvian pathologist, in 1954.