Response to Cabozantinib in Patients with RET Fusion-Positive Lung Adenocarcinomas

Abstract The discovery of RET fusions in lung cancers has uncovered a new therapeutic target for patients whose tumors harbor these changes. In an unselected population of non–small cell lung carcinomas (NSCLCs), RET fusions are present in 1% to 2% of cases. This incidence increases substantially, however, in never-smokers with lung adenocarcinomas that lack other known driver oncogenes. Although preclinical data provide experimental support for the use of RET inhibitors in the treatment of RET fusion-positive tumors, clinical data on response are lacking. We report preliminary data for the first three patients treated with the RET inhibitor cabozantinib on a prospective phase II trial for patients with RET fusion-positive NSCLCs (NCT01639508). Confirmed partial responses were observed in 2 patients, including one harboring a novel TRIM33–RET fusion. A third patient with a KIF5B–RET fusion has had prolonged stable disease approaching 8 months (31 weeks). All three patients remain progression-free on treatment. Significance: Driver oncogene discovery in lung cancers has dramatically changed today's therapeutic landscape. This report of the activity of cabozantinib in RET fusion-positive disease provides early clinical validation of RET fusions as drivers in lung cancers and suggests that RET inhibition may represent a new treatment paradigm in this molecular cohort. Cancer Discov; 3(6); 630–5. ©2013 AACR. See related commentary by Gainor and Shaw, p. 604 This article is highlighted in the In This Issue feature, p. 591