FOXL2 Mutation Analysis of Ovarian Sex Cord-Stromal Tumors: Genotype-Phenotype Correlation With Diagnostic Considerations.

Correlation of FOXL2 mutation status with morphologic features and reticulin staining patterns was performed in a comprehensive single-institutional cohort of ovarian sex cord-stromal tumors. Fifty-one cases were included, 35 of which were morphologically diagnosed as adult granulosa cell tumor, 4 as Sertoli-Leydig cell tumor, 11 as fibroma/fibrothecoma and 1 as a thecoma. Of the adult granulosa cell tumors, 31 (88.6%) harbored FOXL2 mutation. Abundant pale cytoplasm was seen in 51.6% (16/31) of FOXL2 mutated tumors, compared with 6.7% (1/15) among FOXL2 wild type tumors (P=0.003). Nearly half of FOXL2 negative tumors showed individual pericellular reticulin staining pattern, while none of the FOXL2 positive cases demonstrated this feature (P=0.0001). Nested reticulin pattern was observed in 67.7% of FOXL2 positive tumors, compared with 20% of FOXL2 negative cases (P=0.004). Indeterminate reticulin staining pattern was seen in nearly one third of cases in both groups. Nested reticulin pattern was 87.5% specific and 67.7% sensitive for FOXL2 mutation, while individual reticulin pattern was 100% specific for absence of FOXL2 mutation. No statistical significance was observed between the 2 groups in tumor size, mitotic activity, nuclear atypia, and nuclear grooves. Follow-up was available for 44 patients ranging from 0.3 to 259 months (mean: 67.5 mo). Two patients developed recurrence, both of them harbored FOXL2 mutation. In conclusion, the pathology diagnosis of sex cord-stromal tumors continues to be difficult, and reticulin staining remains a valuable tool as an initial step in the diagnostic work-up. Individual pericellular reticulin pattern essentially rules out adult granulosa cell tumor, while cases with indeterminate or nested patterns can be subjected to FOXL2 mutation testing to aid the diagnosis.