FOXL2 402C>G Mutation Can Be Identified in the Circulating Tumor DNA of Patients with Adult-Type Granulosa Cell Tumor

Abstract

Adult granulosa cell tumors (AGCTs) of the ovary are molecularly characterized by the pathognomonic FOXL2 402C>G (C134W) mutation. To improve diagnostics and follow-up, we developed a specific digital droplet PCR (ddPCR) assay to detect the FOXL2 mutation in the circulating tumor DNA (ctDNA) of AGCT patients. Optimization of the ddPCR assay was performed using a TaqMan primer/probe with the RainDance RainDrop digital PCR system. The ddPCR assay was performed on circulating cell-free DNA extracted from 120 serial plasma samples collected prospectively from 35 AGCT patients. The ddPCR assay included a preamplification step that is sensitive and specific for detecting the FOXL2-mutated ctDNA at levels as low as 0.05%. FOXL2 ctDNA mutations were detected in the plasma of 12 of 33 AGCT patients (36%), with both primary (6 of 17, 35%) and recurrent (6 of 31, 19%) tumors. The median tumor size was significantly larger in ctDNA mutation-positive compared with mutation-negative samples (13.5 cm versus 7.5 cm; P = 0.003). The ctDNA FOXL2 mutation was detected in four patients without clinical disease, of which one relapsed during follow-up. As proof of concept, we established that specific molecular diagnosis of AGCT and detection of AGCT recurrence can be achieved noninvasively using ctDNA FOXL2 mutation testing. Further studies are needed to determine the clinical value of ctDNA mutation testing.