Immunohistochemical and selected genetic reflex testing of all uterine leiomyosarcomas and STUMPs for ALK gene rearrangement may provide an effective screening tool in identifying uterine ALK-rearranged mesenchymal tumors.

We examined the value of targeted molecular screening for the identification of uterine anaplastic lymphoma kinase (ALK)-rearranged mesenchymal tumors, including ALK immunohistochemistry followed by molecular genetic testing, in all uterine leiomyosarcomas and STUMPs (smooth muscle tumors of uncertain malignant potential). All leiomyosarcoma and STUMP cases diagnosed in a 10-year period (2006-2016) at Charles University Faculty of Medicine in Pilsen were retrieved and reviewed. Of 23 cases, one case (LMS [leiomyosarcoma]) was positive for ALK rearrangement, namely, PPP1CB-ALK fusion gene. No specific histologic features (i.e., lymphocytic infiltrate and stromal edema) were observed in this case. This suggests that inflammatory myofibroblastic tumor (IMT)-like histologic features may not be an initial reliable screening tool in identifying uterine IMT cases. Thus, we proposed a two-step IHC and molecular genetic testing (as a reflex test) for IMT in all uterine LMS and STUMP cases. This will enhance the proper detection of such tumors at the population level and ultimately offer patients available targeted therapies.