The histopathologic features of Adult Granulosa Cell Tumors (AGCTs) are relatively non-specific, resulting in misdiagnosis of other cancers as AGCT, a problem that has not been well characterized. FOXL2 mutation testing was used to stratify 336 AGCTs from three European centers into three categories: 1) FOXL2 mutant molecularly defined AGCT (MD-AGCT)(n=256 of 336), 2) FOXL2 wild-type AGCT (n=17 of 336), 3) misdiagnosed other tumor types (n=63 of 336). All statistical tests were two-sided. The overall and disease-specific survival of the misdiagnosed cases was lower than in the MD-AGCTs (P