Vulvovaginal Myxoid Epithelioid Smooth Muscle Tumor With NCOA2 Rearrangement: Case Report and Literature Review.

Vulvovaginal myxoid epithelioid smooth muscle tumor with NCOA2 rearrangement is an emerging, rare mesenchymal neoplasm of the female genital tract. We reported a 56-yr-old Chinese woman with a slow-growing, tender mass in the right labium majus. The tumor was composed of epithelioid and spindle cells with smooth muscle differentiation arranged in short fascicles or small nests with prominent myxoid stroma and distinct microcystic formation. The tumor cells were strongly positive for smooth muscle actin, desmin, and caldesmon, negative for estrogen receptor, and had a low Ki-67 labeling index (~1%). Fluorescence in situ hybridization indicated NCOA2 rearrangement, but no MEF2D rearrangement. Our case expands the spectrum of this rare entity with regard to negative estrogen receptor and highlights the value of molecular testing for accurate diagnosis.