EML4::ALK fusions in complex lymphatic malformations.

Gorham-Stout disease (GSD) and generalized lymphatic anomaly (GLA) are subtypes of complex lymphatic malformations (CLMs) with osseous involvement that cause significant complications, including pain and pathologic fractures. As with other vascular anomalies, somatic mosaic mutations in oncogenes are often present, and the mTOR inhibitor sirolimus alleviates symptoms in some, but not all, patients. We describe two patients, one with GSD and one with GLA, found to have EML4::ALK fusions. This report of a targetable, oncogenic fusion in vascular malformations expands our understanding of the genetic basis for CLMs and suggests additional targeted therapies could be effective.