"Deciduoid" Change in Uterine Leiomyomas in Pregnancy: Aberrant Expression of Sex Cord Markers Inhibin and Calretinin.

Leiomyomas are common hormone-responsive uterine neoplasms which can exhibit a variety of morphologic changes secondary to hormonal agents such as progestogens. They may increase in size during pregnancy as a result of hormonal stimulation but surprisingly the morphologic features of leiomyomas in pregnancy are not well described in the literature. In this report, we describe the morphologic features of a series of 29 uterine leiomyomas in pregnancy. The features include in decreasing order of frequency infarct-type necrosis, decidualization of the serosal surface, hyalinization, myxoid alteration of the stroma, edema (sometimes with cyst formation), and dystrophic calcification. We also report a feature which we term "deciduoid" change (seen in 10 of 29 leiomyomas) which takes the form of altered smooth muscle cells with an epithelioid morphology with abundant eosinophilic or clear cytoplasm. Furthermore, we show that the "deciduoid" cells commonly exhibit expression of sex cord markers inhibin and calretinin. We speculate on the pathogenesis of the "deciduoid" change which together with its "aberrant" immunophenotype may result in diagnostic problems and consideration of other neoplasms.