Placenta-associated uterine inflammatory myofibroblastic tumor with a novel FBLN1-ALK1 fusion

Abstract

We report a case of placenta-associated uterine inflammatory myofibroblastic tumor (IMT) with a novel FBLN1-ALK1 fusion. A 28-year-old pregnant woman underwent delivery of a healthy infant at 39 weeks via cesarean section. Following expression of the intact placenta, a separate tissue fragment was delivered after a manual swipe of the uterus. Histologic examination of the separate tissue demonstrated a nodular tumor composed of decidualized, spindled cells growing in fascicles with minimal intervening myxoid stroma. A lymphoplasmacytic and neutrophilic infiltrate was present throughout. Immunohistochemistry for ALK1 was positive, with a novel FBLN1-ALK fusion confirmed by a sarcoma fusion assay. A diagnosis of placenta-associated IMT was rendered. While the vast majority of uterine IMTs harbor ALK-rearrangements, the fusion partners tend to differ based on the clinical scenario, with TIMP3 being most common in pregnant patients and IGFBP5 and THBS1 being most prevalent in nonpregnant patients. Like TIMP3, FBLN1 plays a role in the extracellular matrix and is of importance in pregnancy. It is posited herein that the fusion partners in placenta-associated IMT may lead to this tumors’ uniquely excellent prognosis; their role in the extracellular matrix likely results in easy and complete expression of the tumor alongside or shortly after delivery of the placenta.

Keywords

• Inflammatory myofibroblastic tumor
• Placenta
• Pregnancy
• ALK