The role of FOXL2, SOX9, and β-catenin expression and DICER1 mutation in differentiating sex cord tumor with annular tubules from other sex cord tumors of the ovary.

Sex cord tumor with annular tubules (SCTAT) is a highly rare type of ovarian sex cord-stromal tumor (SCST), the diagnosis of which remains to be challenging. The aim of this study was to scrutinize the utility of three immunohistochemical markers including Forkhead box protein 2 (FOXL2), SOX9, and β-catenin and DICER1 mutation status in distinguishing SCTATs from other ovarian SCSTs. Nine cases of SCTAT, 10 Sertoli-Leydig cell tumor (SCLT), 10 adult-type granulosa cell tumor (AGCT), and 8 juvenile-type granulosa cell tumor (JGCT) were included in the study. SCTATs were characterized by diffuse and strong expression of SOX9, focal and weak expression of FOXL2, and the absence of DICER1 mutation. However, AGCTs and JGCTs displayed strong and diffuse expression of FOXL2, focal/no immunoreaction for SOX9. SLCTs generally showed moderate intensity of FOXL2 and SOX9 expression. Nuclear β-catenin expression was observed in none of SLCT, 1/9 of SCTAT, 6/8 JGCT, and 4/10 AGCT cases, respectively. DICER1 hotspot mutation was detected in only 3 cases of SLCT and 2 cases of JGCT. We conclude that in addition to strong and diffuse SOX9 expression, weak/absent expression of FOXL2 is suggestive for the diagnosis of SCTAT. Hence, we suggest that inclusion of these two markers, SOX-9 and FOXL2, to the immunohistochemical panel helps in differentiation of SCTAT from other SCSTs in addition to morphologic findings. We also conclude that SCTATs of the ovary do not harbor DICER1 hotspot mutation.