FOXL2 mutation is prevalent in metastatic adult granulosa cell tumors and is associated with improved survival

Abstract

<h3>Objectives:</h3> Adult granulosa cell tumors (AGCT) of the ovary represent less than 5% of all ovarian tumors. Despite having a favorable prognosis, nearly one-third of women with this diagnosis will recur, and therapeutic options are limited. We aim to describe a molecular profile of AGCT to improve prognostication and elucidate actionable molecular targets. <h3>Methods:</h3> AGCT samples were analyzed using a combination of next-generation sequencing (NGS), immunohistochemistry (IHC) and whole transcriptome sequencing (NovaSeq) (Caris Life Sciences, Phoenix, AZ). PD-L1 expression was tested by SP-142 (Ventana; positive cut-off ≥1%). Microsatellite instability (MSI) was tested by fragment analysis, IHC and NGS. Tumor mutational burden (TMB) was measured by counting all somatic mutations per tumor (TMB-high cut-off ≥10 mutations per MB). Immune cell fraction was calculated by QuantiSeq (Finotello 2019, Genome Medicine). Gene Set Enrichment Analysis (GSEA) was used to determine enrichment of cancer hallmark pathways (Broad Institute). Survival analyses were performed using the Kaplan-Meier estimate. <h3>Results:</h3> Of the 319 patients, the median age was 55, and most patients had metastatic disease (82.4 %). A majority of the tumors carried FOXL2 mutations (83.6%), of which 90% demonstrated a <i>C134W</i> missense mutation. Patients with FOXL2 mutations were significantly older (56 versus 47 years, p=0.003) and more likely to have metastatic disease than patients with wild-type FOXL2 (p=0.045). Other frequent mutations included KMT2D (14%) and PIK3CA (8%) mutations. There were no pathogenic <i>BRCA1</i> or <i>BRCA2</i> mutations identified in this cohort; however, a <i>BRCA2</i> mutation variant of unknown significance was noted in three tumors. Pathway analyses demonstrated that alterations in chromatin remodeling were significantly more common in tumors with FOXL2 mutations compared to wild-type status (16.1% versus 9.7%, p<0.05), as were alterations in the PI3K pathway (13.9% versus 0%, p<0.05). There was a low frequency of PD-L1 high expression (2.7%), and there were no tumors with high TMB or MSI. Patients with tumors with FOXL2 mutations had improved overall survival compared to patients with wild-type FOXL2 tumors (HR 2.07, CI 1.01-4.25, p=0.043). KMT2D and PI3KCA mutations were not associated with differences in overall survival when compared to wild-type tumors. Copy number alterations in the genes GPHN, HOOK3, SPEN, CAMTA1 and BCL2L11 were associated with survival differences in patients treated with bevacizumab. <h3>Conclusions:</h3> A majority of AGCT carry FOXL2 mutations. The next most common mutations were KMT2D, PIK3CA, and alterations in chromatin remodeling. In this cohort of patients, the FOXL2 mutation was associated with improved overall survival. Copy number alterations in specific genes were associated with differences in survival in patients treated with bevacizumab. These results support molecular profiling of AGCT to improve prognostication for these patients. These findings provide groundwork to direct further investigation into novel treatment strategies and targeted agents in AGCT.