FOXL2 Is a Sensitive and Specific Marker for Sex Cord-Stromal Tumors of the Ovary

Abstract

Sex cord-stromal tumors (SCSTs) of the ovary are relatively uncommon tumors. Diagnosis of SCST rests primarily on the histomorphology of these tumors, and tumors with an atypical or unconventional appearance can pose diagnostic challenges. Previously, we had identified FOXL2 (402C→G) mutation as being characteristic of adult granulosa cell tumors (aGCTs). However, molecular screening for this mutation is not always possible and adds time and cost to the diagnostic process. In this study, we investigated the potential diagnostic use of immunostaining for FOXL2 on formalin-fixed paraffin-embedded tissue sections. Using a commercially available polyclonal antiserum against FOXL2 protein, immunoexpression of FOXL2 was tested in 501 ovarian tumor samples, including 119 SCSTs, using whole tissue sections and tissue microarrays. Staining was correlated with FOXL2 mutation status. In addition, we compared FOXL2 immunoexpression with that of α-inhibin and calretinin, the 2 traditional immunomarkers of SCST, in a subset of 89 SCSTs. FOXL2 immunostaining was present in 95 of 119 (80%) SCSTs, including >95% of aGCTs, juvenile granulosa cell tumors, fibromas, and sclerosing stromal tumors. Only 50% of Sertoli-Leydig cell tumors (N=40) expressed FOXL2. One of 11 steroid cell tumors and 3 of 3 female adnexal tumors of probable Wolffian origin showed FOXL2 immunoreactivity, whereas all other non-SCSTs tested (N=368) were negative for FOXL2 expression. Thus, the sensitivity and specificity of FOXL2 immunoreactivity for SCST are 80% and 99%, respectively. The FOXL2 (402C→G) mutation was confirmed to be both a sensitive and relatively specific indicator of aGCT. Forty-five of 119 SCSTs were mutation positive. These cases were 39 of 42 (93%) aGCTs, 3 of 40 Sertoli-Leydig cell tumors, 2 of 5 thecomas, and 1 of 4 (25%) SCSTs of unclassified type. SCSTs harboring a FOXL2 mutation consistently immunoexpressed FOXL2 (44 of 45, 98%), but FOXL2 immunostaining was also seen in many SCSTs that lacked a mutation (49 of 73, 67%). FOXL2 immunostaining showed higher sensitivity for the diagnosis of SCST, compared with α-inhibin and calretinin, and FOXL2 staining was typically more intense in positive cases compared with either α-inhibin or calretinin. In the SCSTs that were negative for FOXL2 expression, α-inhibin and/or calretinin immunostaining yielded positive results. In conclusion, FOXL2 is a relatively sensitive and highly specific marker for SCST. FOXL2 staining is present in almost all SCSTs with a FOXL2 mutation, and also in a majority of SCSTs without a mutation. FOXL2, together with α-inhibin and calretinin, forms an immunomarker panel that will result in positive staining with 1 or more markers in essentially all cases of SCST.

FOXL2 molecular testing in ovarian neoplasms: diagnostic approach and procedural guidelines

“…The majority of adulttype granulosa cell tumors can be accurately diagnosed solely based on the examination of H&E-stained slides; however, even in expert gynecopathology environments there will always be a number of challenging cases in which adult-type granulosa cell tumor enters the differential diagnosis but a definitive diagnosis is not possible based on the examination of routine H&E-stained slides. Following up on the results of our previous study, 3 the current report confirms the utility of a diagnostic strategy including FOXL2 immunohistochemistry and mutation testing in equivocal cases in confirming or excluding a diagnosis of adult-type granulosa cell tumor. The presence of FOXL2 mutation appears to conclusively support a diagnosis of adult-type granulosa cell tumor, based on the available evidence; however, a FOXL2 wildtype result cannot be used to definitively suggest an alternate diagnosis.…”

“…We previously reported a case that was diagnosed, after gynecological pathology review, as thecoma, but recurred 2 years later with histological features of adult-type granulosa cell tumor. 3 Both the original tumor and the recurrence were FOXL2 mutation positive, leading us to conclude that the tumor was misdiagnosed originally, and propose that the rare cases diagnosed as malignant thecoma in the past may have been luteinized adult-type granulosa cell tumors. A correct diagnosis of adult-type granulosa cell tumor in these cases does not change treatment, but does allow for appropriate follow-up.…”

“…The p53 immunohistochemistry in this case was misleading; although uncommon, strong p53 immunostaining can be seen in adult-type granulosa cell tumors; 11,12 p53 was confirmed to be mutated in this case, in both the original tumor and recurrence. Similarly, negative inhibin immunostaining can be seen rarely in adult-type granulosa cell tumors, 3 especially in small tumor samples.…”

“…[1][2][3][5][6][7] To date PubMed indexed reports cite a total of 290 adult-type granulosa cell tumors that have been tested for the FOXL2 mutation of which 267 (92%)…”

“…3 It was the aim of this study to demonstrate how testing for the FOXL2 mutation can be used in a gynecological pathology consultation service in which diagnostic algorithms were applied to prospectively collected cases.…”