Gynecologic tract origin of inflammatory myofibroblastic
tumor (IMT), a
receptor tyrosine kinase fusion driven
tumor with malignant potential, is uncommon and mostly involves the uterine corpus where misclassification as a
smooth muscle tumor may occur due to overlapping morphologic features. With rare exception, uterine IMT involves ALK rearrangements and exhibits ALK immunoexpression. Molecularly confirmed vulvovaginal IMT has not been reported, but several low-grade mesenchymal
tumors in this region exhibit myxoid stroma and/or inflammatory infiltrates that may resemble IMT. The aims of this study were to define the diagnostic specificity of ALK immunoexpression for IMT among a broad spectrum (107 cases) of vulvovaginal mesenchymal
tumors in the differential diagnosis of IMT and to report the clinicopathologic features of vulvovaginal IMT identified in our archives or via retrospective ALK staining of otherwise classified vulvovaginal
tumors. Review of archives from 5 different centers revealed a single case of vulvar IMT in a 62-yr-old woman. The 2.5 cm well-circumscribed
tumor exhibited the typical microscopic features of IMT, namely a loose fascicular distribution of bland spindle cells within a myxoid stroma, accompanied by an infiltrate of plasma cells, lymphocytes, and eosinophils. The
tumor cells exhibited expression for smooth muscle actin,
desmin, h-
caldesmon, and ALK. Break-apart fluorescence in situ hybridization confirmed the presence of ALK rearrangement. The patient did not receive any treatment and is alive without disease 32 mo later. No evidence of ALK expression was detected in any of the other 107 vulvovaginal
tumors, which included 14 aggressive
angiomyxomas, 2 superficial
angiomyxomas, 12 angiomyofibroblastomas, 8 cellular
angiofibromas, 15 smooth muscle
neoplasms, 10
peripheral nerve sheath tumors, 20 fibroepithelial
polyps, and a variety of other low grade mesenchymal
tumors. Although vulvovaginal ALK- rearranged IMT is exceedingly rare, the behavior remains to be fully understood. ALK immunohistochemistry, which appears specific for IMT in this anatomic site, is advised in the evaluation of vulvovaginal mesenchymal
tumors exhibiting myxoid stroma and/or an inflammatory infiltrate.