Reduced folate receptor alpha (FOLR1) protein expression in fallopian tubes from premenopausal women: implications for the FOLR1 CDx assay for mirvetuximab-soravtansine therapy.

Background:Survivin is an oncoprotein silenced in normal mature tissues but reactivated in serous ovarian cancer (SOC). Although transcriptional activation is assumed for its overexpression, the long 3'-untranslated region (3'-UTR) in survivin gene, which contains many alternate polyadenylation (APA) sites, implies a propensity for posttranscriptional control and therefore was the aim of our study.Methods:The abundance of the coding region, the proximal and the distal region of survivin mRNA 3'-UTR, was evaluated by real-time polymerase chain reaction (PCR) in SOC samples, cell lines, and normal fallopian tube (NFT) tissues. The APA sites were confirmed by rapid amplification of cDNA 3' ends and DNA sequencing. Real-time PCR were used to screen survivin-targeting microRNAs (miRNAs) that were inversely correlated with survivin. The expression of an inversely correlated miRNA was restored by pre-miRNA transfection or induction with a genotoxic agent to test its inhibitory effect on survivin overexpression.Results:Varying degrees of APA were observed in SOC by comparing the abundance of the proximal and the distal region of survivin 3'-UTR, and changes of 3'-UTR correlated significantly with survivin expression (r = 0.708, P < 0.01). The main APA sites are proved at 1197 and 1673 of survivin 3'-UTR by DNA sequencing. Higher level of 3'-UTR proximal region than coding region was observed in NFT, as well as in SOC and cell lines. Among the survivin-targeting miRNAs, only a few highly expressed miRNAs were inversely correlated with survivin levels, and they mainly targeted the distal part of the 3'-UTR. However, in ovarian cancer cells, restoration of an inversely correlated miRNA (miR-34c) showed little effect on survivin expression.Conclusions:In NFT tissues, survivin is not transcriptionally silenced but regulate posttranscriptionally. In SOC, aberrant APA leads to the shortening of survivin 3'-UTR which enables it to escape the negative regulation of miRNAs and is responsible for survivin up-regulation.

Mirvetuximab soravtansine is an anti-FOLR1 (folate receptor 1/alpha) antibody-drug conjugate with a companion diagnostic immunohistochemical (IHC) biomarker for platinum-resistant ovarian, fallopian tube and primary peritoneal carcinoma. Its effectiveness has sparked interest in FOLR1 expression in endometrial carcinoma. We evaluate the relationship of FOLR1 and HER2-IHC expression in high-grade p53-aberrantly expressed endometrial carcinomas, as overexpression of both is associated with high-grade histologic features and aggressiveness. Carcinomas were scored for HER2-IHC by both gastric and endometrial serous criteria and FOLR1-IHC by Ventana package insert on tissue microarray cores. Intratumoral heterogeneity was quantified for HER2 and FOLR1 expression across multiple cores from the same tumour. A total of 291 cores (226 endometrial serous, 47 high-grade endometrioid and 18 high-grade Müllerian carcinoma, nos) were collected from 66 cases (discrete accession dates) from 62 patients. When stratified by two-category HER2-IHC status (0/1+ vs. 2+/3+, either criteria), significantly more HER2 2+/3+ cores (16/133, 12%) were FOLR1-positive by a ≥75% cut-off than HER2 0/1+ specimens (8/158, 5%, P = 0.031). Results were similar by a ≥25% cut-off (49/133, 37% vs. 38/158, 24%; P = 0.018). More cases with high HER2-IHC heterogeneity (2-3-pt difference) also demonstrated FOLR1-IHC heterogeneity (≥50% score difference between cores from the same case) than cases with no or low (1-pt) HER2-IHC heterogeneity, though most cases did not show high HER2 or FOLR1 intratumoral heterogeneity (16.7%-18.2% 2-3-pt difference and 12.1% ≥50% score difference). A positive correlation between HER2 and FOLR1 overexpression may be seen in high-grade endometrial carcinomas with aberrant p53 expression, which may extend to intratumoral heterogeneity of biomarker expression.

Introduction: The histologically normal BRCA1 mutation carrier fallopian tube epithelia (FTE), compared to controls, showed that CEBPD was upregulated in the luteal phase of the ovulatory cycle. CEBPD is involved with the maintenance of genomic stability, promoting cellular differentiation, and regulating the cell cycle in response to cytotoxic stressors. In breast epithelial cells, CEBPD protein expression correlated with estrogen receptor (ER) and progesterone receptor (PR) and was found to be associated with increased progression-free survival in breast cancer patients. In fallopian tube epithelia (FTE), CEBPD was also found to modulate the epithelial-to-mesenchymal (EMT)/mesenchymal-to-epithelial transition (MET) by modulating target genes of this pathway. Given the hormonal response of this gene and its function in modulating an EMT/MET, the objective of this study was to determine whether sex hormones influence CEBPD regulation of EMT/MET in the fallopian tube and thus ovarian cancer. Methods: Fresh fallopian tube (FTE) tissues were obtained from patients approved for collection by IRB. Immunohistochemical profiling on normal fallopian tube tissue and HGSC was performed using CEBPD, ER, and PR protein markers. FTE cell lines with a p53 mutation (R175H) were subjected to estradiol (50nM and 100nM) and 4-hydroxytamoxifen (10nM) and assayed using qRT-PCR and PCR. ANOVA and t-tests were conducted in GraphPad Prism software with significance set at p&amp;lt;0.05. Results: E-cadherin in normal fallopian tube tissue was highly expressed in both the luteal and follicular phase whereas vimentin was highly expressed in the follicular phase but showed a range of expression (low expression to high expression) in the luteal phase. CEBPD overexpression increased SNAIL expression (p&amp;lt;0.0001), consistent with previous findings; treatment with 50nM estradiol (E2) resulted in increased SNAIL and SLUG mRNA expression in FTE cell lines overexpressing CEBPD (p&amp;lt;0.0001) relative to controls and decreased ZEB1 and ZEB2 mRNA expression. Addition of tamoxifen to cells overexpressing CEBPD increased SNAIL mRNA expression compared to cells without tamoxifen (p&amp;lt;0.0001); however, a combination of both tamoxifen and estradiol added to these cells decreased SNAIL expression relative to controls. IL6 mRNA expression level was increased in CEBPD overexpressing cells compared to controls (p&amp;lt;0.0001), which was further increased by E2 (p&amp;lt;0.0001). Conclusion: Together these results demonstrate a role for CEBPD in modulating EMT/MET in normal FTE in a hormonally regulated manner, which during cancer formation and spread is critical for anoikis and metastasis. Furthermore, these data will facilitate an understanding of the early events of carcinogenesis in fallopian tube epithelia. Citation Format: Ramlogan Sowamber, Leah V. Dodds, Patricia Shaw, Sophia H.L. George. Ovarian hormones regulate C/EBPD induced EMT/MET transition in the human fallopian tube epithelia [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B29.

Low-grade serous ovarian cancer is a rare epithelial ovarian cancer subtype characterized by high resistance to chemotherapy. Development of novel, effective, targeted treatments for recurrent low-grade serous ovarian cancer remains an unmet medical need. We evaluated FOLR1 expression in a cohort of low-grade serous ovarian cancer patients and the preclinical and clinical activity of mirvetuximab soravtansine, an antibody-drug conjugate targeting FOLR1, in vivo in a patient-derived xenograft model and in a heavily pretreated low-grade serous ovarian cancer patient progressing after chemotherapy, aromatase inhibitor, and MEK inhibitor treatment. FOLR1 expression was evaluated in 27 low-grade serous ovarian cancer patients using immunohistochemistry. The efficacy of mirvetuximab soravtansine was assessed in vivo in a low-grade serous ovarian cancer patient-derived xenograft model in severe combined immunodeficient mice, as well as in a patient harboring a recurrent low-grade serous ovarian cancer resistant to standard treatment modalities. FOLR1 expression was detected in all 27 (100%) low-grade serous ovarian cancer cases, with 21 of 27 (78%) of the samples demonstrating 2+/3+ in ≥75% of tumor cells. In vivo studies in mice demonstrated that mirvetuximab soravtansine inhibited tumor growth and prolonged survival in a low-grade serous ovarian cancer patient-derived xenograft model derived from a patient progressing after chemotherapy/aromatase inhibitor/MEK inhibitor. Clinical evidence further supported the therapeutic activity of mirvetuximab soravtansine in a FOLR1-positive low-grade serous ovarian cancer patient, as indicated by a prolonged partial response after 8 months of treatment. FOLR1 is overexpressed in a large percentage of low-grade serous ovarian cancers. Mirvetuximab soravtansine may represent a novel treatment option for low-grade serous ovarian cancer patients progressing after standard treatment modalities. Clinical trials with mirvetuximab soravtansine in FOLR1-positive low-grade serous ovarian cancers are warranted.

ObjectiveWith the development of novel antibody-drug conjugates (ADCs), folate receptor alpha (FOLR1) is a promising therapeutic target for the treatment of platinum-resistant tubo-ovarian carcinomas. The main aims of this study were to assess FOLR1 protein expression in a large cohort of ovarian carcinoma histotypes. To inform future clinical trial design we identified molecular correlates of FOLR1 expression in low-grade serous carcinoma (LGSC).MethodsOne thousand five hundred forty-seven ovarian carcinoma samples from 5 different Canadian cohorts were successfully evaluated by immunohistochemistry for FOLR1 expression using the PS2+ system. Statistical analyses with clinicopathological parameters, LGSC molecular subtypes, and overall survival (OS) were performed.ResultsHigh FOLR1 expression was detected in 44% of high-grade serous carcinomas, and in 30% LGSC, 8% clear cell, 6% endometrioid, and 0% mucinous and/or mesonephric-type adenocarcinomas. In 160 LGSC cases, FOLR1 expression was more frequent in cases with normal MAPK pathway status (37% MAPK wild type vs. 14% canonical MAPK pathway mutations; p=0.002), low progesterone receptor (PR) expression (41%) vs. 23% (Allred score >2; p=0.02), and p16 loss (48% p16 absent vs. 26% normal; p=0.03). Canonical MAPK mutation status and PR expression remained significant on multivariable analysis. No significant associations between OS and FOLR1 expression were observed.ConclusionA significant proportion of LGSC express high FOLR1 levels supporting the development of clinical trials to investigate ADCs targeting FOLR1 as novel agents for treating this disease. In LGSC, high FOLR1 expression was associated with fewer MAPK pathway alterations, low PR expression, and p16 loss.

Sudden cardiac death in women: causes of death at premenopausal and postmenopausal age

IntroductionElafin is an endogenous serine protease inhibitor. The majority of breast cancer cell lines lack elafin expression compared to human mammary epithelial cells. In this study, we hypothesized that elafin is downregulated during breast and ovarian tumorigenesis.MethodsWe examined elafin expression by immunohistochemistry (IHC) in specimens of normal breast tissue (n = 24), ductal carcinoma in situ (DCIS) (n = 54), and invasive breast cancer (n = 793). IHC analysis of elafin expression was also performed in normal fallopian tube tissue (n = 20), ovarian cystadenomas (n = 9), borderline ovarian tumors (n = 21), and invasive ovarian carcinomas (n = 216). To understand the significance of elafin in luminal breast cancer cell lines, wild-type or M25G elafin (lacking the protease inhibitory function) were exogenously expressed in MCF-7 and T47D cells.ResultsElafin expression was downregulated in 24% of DCIS and 83% of invasive breast tumors when compared to elafin expression in the normal mammary epithelium. However, the presence of elafin-positive cells in invasive breast tumors, even at low frequency, correlated with poor recurrence-free survival (RFS), reduced overall survival (OS), and clinicopathological markers of aggressive tumor behavior. Elafin-positive cells were an especially strong and independent prognostic marker of reduced RFS in IHC-defined luminal A-like tumors. Elafin was also downregulated in 33% of ovarian cystadenomas, 43% of borderline ovarian tumors, and 86% of invasive ovarian carcinomas when compared to elafin expression in the normal fallopian tube. In ovarian tumors, elafin-positive cells were correlated with reduced RFS, OS and disease-specific survival (DSS) only in stage I/II patients and not in stage III/IV patients. Notably, exogenous expression of elafin or elafin M25G in the luminal breast cancer cell lines MCF-7 and T47D significantly decreased cell proliferation in a protease inhibitory domain-independent manner.ConclusionsElafin predicts poor outcome in breast and ovarian cancer patients and delineates a subset of endocrine receptor-positive breast cancer patients susceptible to recurrence who could benefit from more aggressive intervention. Our in vitro results suggest that elafin arrests luminal breast cancer cells, perhaps suggesting a role in tumor dormancy.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0497-4) contains supplementary material, which is available to authorized users.

To investigate the expression of Talin1 in the fallopian tube and chorionic villi in patients with tubal pregnancy and its role in regulating invasion and migration of trophoblasts. Immunohistochemistry and Western blotting were used to detect the localization and expression level of Talin1 in the fallopian tube and chorionic villi in patients with tubal pregnancy and in women with normal pregnancy. In the cell experiment, HTR-8/SVneo cells was transfected with Talin1 siRNA and the changes in cell invasion and migration were assessed using scratch assay and Transwell assay. The expressions of MMP-2, MMP-9, N-cadherin and Snail in the transfected cells were detected by qRT-PCR and Western blotting. Positive expression of Talin1 was detected in both normal fallopian tube tissues and tissues from women tubal pregnancy, and its expression was localized mainly in the cytoplasm of cilia cells. The expression level of Talin1 was significantly higher in both the fallopian tube and chorionic villi in women with tubal pregnancy than in normal fallopian tube and chorionic villi samples (P < 0.01). In HTR-8/SVneo cells, transfection with Talin1 siRNA significantly inhibited cell invasion (P < 0.01) and migration (P < 0.05), down-regulated the expression of N-cadherin, MMP-2 and Snail (P < 0.05), and up-regulated the expression of MMP-9 in the cells (P < 0.05). The expression of Talin1 in the fallopian tube and chorionic villi is significantly increased in women with tubal pregnancy, suggesting the association of Talin1-regulated trophoblast cell invasion with the occurrence of tubal pregnancy.

Elafin is an endogenous serine protease inhibitor. The majority of breast cancer cell lines lack elafin expression compared to human mammary epithelial cells. In this study, we hypothesized that elafin is downregulated during breast and ovarian tumorigenesis. We examined elafin expression by immunohistochemistry (IHC) in specimens of normal breast tissue (n = 24), ductal carcinoma in situ (DCIS) (n = 54), and invasive breast cancer (n = 793). IHC analysis of elafin expression was also performed in normal fallopian tube tissue (n = 20), ovarian cystadenomas (n = 9), borderline ovarian tumors (n = 21), and invasive ovarian carcinomas (n = 216). To understand the significance of elafin in luminal breast cancer cell lines, wild-type or M25G elafin (lacking the protease inhibitory function) were exogenously expressed in MCF-7 and T47D cells. Elafin expression was downregulated in 24% of DCIS and 83% of invasive breast tumors when compared to elafin expression in the normal mammary epithelium. However, the presence of elafin-positive cells in invasive breast tumors, even at low frequency, correlated with poor recurrence-free survival (RFS), reduced overall survival (OS), and clinicopathological markers of aggressive tumor behavior. Elafin-positive cells were an especially strong and independent prognostic marker of reduced RFS in IHC-defined luminal A-like tumors. Elafin was also downregulated in 33% of ovarian cystadenomas, 43% of borderline ovarian tumors, and 86% of invasive ovarian carcinomas when compared to elafin expression in the normal fallopian tube. In ovarian tumors, elafin-positive cells were correlated with reduced RFS, OS and disease-specific survival (DSS) only in stage I/II patients and not in stage III/IV patients. Notably, exogenous expression of elafin or elafin M25G in the luminal breast cancer cell lines MCF-7 and T47D significantly decreased cell proliferation in a protease inhibitory domain-independent manner. Elafin predicts poor outcome in breast and ovarian cancer patients and delineates a subset of endocrine receptor-positive breast cancer patients susceptible to recurrence who could benefit from more aggressive intervention. Our in vitro results suggest that elafin arrests luminal breast cancer cells, perhaps suggesting a role in tumor dormancy.

To analyze the expression trends and clinical significance of Apurinic/Apyrimidinic Endodeoxyribonuclease 1 (APE1/Ref-1) and Nucleophosmin (NPM1) proteins in high-grade serous ovarian adenocarcinoma (HGSC). The expressions of APE1/Ref-1 and NPM1 proteins in 94 patients with HGSC were determined using the immunohistochemical (IHC) method, and their relationships with clinicopathological features were analyzed by the χ2 test or Fisher's exact test. The follow-up data, Cox proportional hazards univariate and multivariate survival analyses were integrated to evaluate the prognostic factors affecting patients with HGSC. In the normal fallopian tubes, APE1/Ref-1 and NPM1 protein were mainly distributed in the nuclear. The HGSC experienced changes in the cellular localization of APE1/Ref-1 and NPM1 protein expressions, which were abnormally expressed in the cytoplasm. The rates of abnormal cytoplasmic expression of APE1/Ref-1 and NPM1 proteins in 94 patients with HGSC were 69.1% and 73.4%, respectively, which were significantly higher than the normal fallopian tube tissues (p < 0.05). The abnormal cytoplasmic APE1/Ref-1 and NPM1 are significantly correlated with the lymph node metastasis, chemosensitivity, FIGO staging, and prognosis. The COX multivariate survival analysis showed that the abnormal expression of APE1/Ref-1 protein, FIGO staging, and lymph node metastasis are independent prognostic factors. Collectively, the abnormal cytoplasmic APE1/Ref-1 and NPM1 proteins are associated with the oncogenic progression and chemoresistance of HGSC, and predict a poor prognosis.

Background: Ovarian cancers are the most common gynecologic malignancies. Low grade serous ovarian carcinoma (LGSOC) is a rare tumor, accounting for ~2000 cases diagnosed every year in North America. Most of LGSOCs are characterized by high fatality rates over the long term, with only 20% of women surviving 10 years after diagnosis, due suboptimal response to current chemotherapies. Understanding the molecular events is crucial for developing better early detection strategies and more informed therapeutic options. LGSOC harbors a relatively stable genome, with common activating mutations in BRAF, KRAS and NRAS. Recently, NRAS mutations (Q61R) were found to co-exist with EIF1AX mutations (G8E) in LGOSC, and the two mutated proteins functionally cooperate. Increasing histological and gene expression evidence suggest that the cell of origin of LGSOC is in the Fallopian tube. Low incidence of this disease means it is poorly understood, and the resulting lack of available models further limits the study of underlying mechanisms. We therefore propose to use organoid cultures. These consist of 3D multicellular units that resemble in vitro a tissue or organ of body, both structurally and functionally. Objective: to elucidate molecular events underpinning LGSOC, specifically how NRAS(Q61R) and EIF1AX (G8E) mutations co-operate to drive early stages of tumorigenesis, with organoid system and single-cell RNA sequencing (scRNA-seq) technologies. Method: To reflect genetic background and cell of origin of LGSOC, NRAS Q61R and EIF1AX G8E mutant proteins were overexpressed via lentiviral transduction in organoid cultures of normal human Fallopian tubes. After allowing organoids to establish, 2 weeks after transduction gene expression alterations were resolved with scRNA-seq. Histology of organoids were assessed for histomorphological signs of transformation. Patient-derived tumor organoids (PDTOs) were also cultured to assess how well our LGSOC-modelling organoids (LMOs) recapitulate the histological features of patient tumours. Result: LMOs showed cytologic signs of transformation such as increased nuclear/cytoplasmic ratio, prominent nucleoli, and cellular pleomorphism. Papillary structures, a major histologic characteristic of LGSOC tumor were also observed in LMOs. PDTOs showed similar cytological features and organization as LMOs. From scRNA-seq, we identified genes up-regulated in double-mutant compared to single-mutant organoids such as CA125 and TACSTD2. CA125 is one of the earliest identified biomarkers for ovarian cancer and has remained to be the most useful serum marker despite limited sensitivity and specificity; whereas TACSTD2 overexpression has been found to correlate with a chemo-resistant, aggressive malignant phenotype. Conclusion and future directions: Organoid culture and scRNA-seq is a powerful duo in studying early tumorigenesis events. We established a novel model system of LGSOC by introducing common co-occurring mutations into normal Fallopian tube tissues. Our model recapitulates to a large extent of LGSOC histology. Genes upregulated in double mutants included well-characterized biomarker (CA125) and a potential biomarker or therapeutic target (TACSTD2). Our work will be crucial for developing early detection strategies and targeted treatment options. Citation Format: Joyce Yu Han Zhang, Dawn Cochrane, Kieran Campbell, Minh Bui, Germain Ho, Cindy Shen, Winnie Yang, Clara Salamanca, Genny Trigo, David G. Huntsman. Investigating mutation co-operativity in early tumorigenesis of low-grade serous ovarian carcinoma with organoid model system and single-cell RNA sequencing [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4899.

BackgroundFolate receptor alpha (FOLR1/FRA) is expressed in a number of epithelial cancers and in particular epithelial ovarian cancer (EOC), especially of the serous histotype. Recent studies have shown that EOC originates from the fallopian tube fimbriae rather than from epithelial cells lining the ovary. We have previously shown by immunohistochemistry a strong correlation between FRA expression in EOC and normal and fallopian adenocarcinoma. Folate receptor beta (FOLR2/FRB) has been described to be expressed by macrophages both in inflammatory disorders and certain epithelial cancers. Given the high sequence identity of these two folate receptor family members we sought to investigate the architectural and cell-specific expression of these two receptors in gynecologic tissues.MethodsRNA scope, a novel chromogenic in situ hybridization assay tool, was used to examine expression of the alpha (FOLR1) and beta (FOLR2) isoforms of folate receptor relative to each other as well as to the macrophage markers CD11b and CD68, in samples of normal fallopian tube and fallopian adenocarcinoma as well as normal ovary and EOC.ResultsWe demonstrated expression of both FOLR1 and FOLR2 in EOC, normal fallopian tube and fallopian adenocarcinoma tissue while very little expression of either marker was observed in normal ovary. Furthermore, FOLR2 was shown to be expressed almost exclusively in macrophages, of both the M1 and M2 lineages, as determined by co-expression of CD11b and/or CD68, with little or no expression in epithelial cells.ConclusionsThese findings further substantiate the hypothesis that the cell of origin of EOC is tubal epithelium and that the beta isoform of folate receptor is primarily restricted to macrophages. Further, macrophages expressing FOLR2 may represent tumor associated or infiltrating macrophages (TAMs) in epithelial cancers.

Volumetric quantification of the effect of aging and hormone replacement therapy on breast composition from digital mammograms

5561 Background: Targeted therapy in folate receptor alpha (FOLR1)-positive high grade serous ovarian carcinoma (HG) is now a mainstay for platinum-resistant disease, though the rate of FOLR1-positivity in low grade serous ovarian carcinoma (LG) is unknown. We compared the genomic and transcriptomic landscapes in FOLR1-positive/negative LG in comparison to its HG counterpart. Methods: LG (N = 281) and HG (N = 5086) tumors were tested at Caris Life Sciences (Phoenix, AZ) with NextGen Sequencing on DNA (592 genes or whole exome) and RNA (whole transcriptome). PD-L1+ (22C3, TPS &gt; 1%) and FOLR1 (Positive [F+], ⩾ 2+, ⩾75%) expression was assessed by IHC. Mutations were defined as pathogenic SNVs/indels (-Mt). Transcriptomic signatures associated with response to immunotherapy (T cell-inflamed) or with MAPK pathway activation (MPAS) were applied. Fisher’s exact/χ2 and Mann-Whitney U tests were applied as appropriate ( p &lt; .05, adjusted for multiple comparisons). Real-world overall survival (OS) was obtained from insurance claims and Kaplan-Meier estimates were calculated for molecularly defined patients. This study was reviewed by the Johns Hopkins Medicine IRB and determined to qualify as exempt human subjects research. Results: HG tumors had a higher prevalence of F+ tumors (43.5%) as compared to LG (24.6%). HG tumors had a higher prevalence of TP53-Mt compared to LG (LG F+: 11.1%, LG F-: 4.1, HG F+: 97.1, HG F-: 95.6, p &lt; .001). Conversely, KRAS-Mt and NRAS-Mt were enriched in LG tumors (KRAS [LG F+: 22.2%, LG F-: 21.6, HG F+: 0.4, HG F-: 3.3, p &lt; .001], NRAS [LG F+: 0%, LG F-: 10.2, HG F+: 0.2, HG F-: 0.1, p &lt; .001]). BRAF-Mt were also almost exclusively present in LG tumors although more prevalent in LG F- as compared to LG F+ (LG F+: 7.4%, LG F-: 14.3, HG F+: 0.2, HG F-: 0.3, p &lt; .001). There was a higher prevalence of PDL1+ tumors in HG vs LG (LG F+: 39.3%, LG F-: 35.9, HG F+: 70.0, HG F-: 72.4, p &lt; .001). LG tumors had a significantly higher MPAS than HG tumors (LG F+: 1.38 arbitrary units, LG F-: 1.66, HG F+: -0.35, HG F-: -0.25, p &lt; .001). LG F- and HG F- tumors had a similar proportion of T cell-inflamed tumors (LG F-: 36 vs HG F-: 33, p &gt; .05), whereas LG F+ tumors have a significantly lower proportion of T cell-inflamed tumors as compared to HG F+ (LG F+: 18% vs HG F+: 42, p &lt; .001). Amongst tumors that had not received mirvetuximab soravtansine, no difference in OS was observed between HG F- v HG F+ (HR 1.3, p = .072; median OS HG F-: 87 months [N = 1092], HG F+: 98 [N = 756]). No difference in OS was observed when comparing LG F- vs LG F+ (HR 1.0 , p = .93; median OS LG F-: 98 months [N = 116], LG F+: not reached [N = 37]). Conclusions: A notable portion of LG tumors were FOLR1+, which suggests that FOLR1 expression in LG could be a viable target for this rare histology, particularly in the recurrent setting. MAPK activation was significantly higher in LG tumors when compared to HG, yet no difference between LG F+ and F- tumors was observed.

3136 Background: Mirvetuximab soravtansine is an antibody–drug conjugate currently approved for the treatment of advanced platinum-resistant ovarian cancer. The efficacy of this therapy is correlated with high expression of folate receptor alpha (FRα), encoded by the FOLR1 gene. Treatment requires ≥ 75% of tumor cells to be stained positively for FRα by immunohistochemistry (IHC). Here we defined the FOLR1 RNA level that distinguishes ovarian cancers with very high FRα (≥ 75% by IHC), then compared the transcriptomic profile of these cases (FOLR1-H) with the transcriptomic profile of cases with very low FRα expression (FOLR1-L). We further explored the presence similar FOLR1-H signature in various types of cancers. Methods: RNA was extracted from 1450 solid tumor FFPE samples and sequenced using a targeted RNA panel of 1600 genes. The RNA expression levels of various genes were quantified and expressed as transcript per million (TPM). IHC for FRα protein was performed on ovarian cancers (N = 49) using VENTANA FOLR1 RxDx assay. Results: Based on comparing IHC with RNA expression of FOLR1, FOLR1-H samples were defined with RNA ≥ 300 TPM while FOLR1 mRNA &lt; 100 was correlated with very low FRα by IHC and classified as FOLR1-L. Of the 312 ovarian cancers, 21% were classified as FOLR1-H and showed significantly (Log10FDR &lt; -2) higher expression in 39 genes as compared with FOLR1-L. The Log10FDR was &lt; -10 in 19 genes. The top highly expressed genes in FOLR1-H cases were TROP2, NECTIN4, ROR1, ROR2, ACVRL1, and NTHL1. In breast cases (N = 199) FOLR1-H was detected in 14.6% of cases and the most highly expressed genes were ACVRL1, NECTIN4, ROR1, and ACVRL1 (Log10FDR &lt; -5). Of the 932 cases of lung cancer, 21.5% classified as FOLR1-H and had significantly (Log10FDR &lt; -2) high expression of 137 genes, but similar to ovarian cancer TROP2, NECTIN4, ROR1, ROR2, ACVRL1, and NTHL1 were top expressed genes. Of the 174 pancreatic cancers 9.8% were FOLR1-H and top expressed genes were NECTIN4, ROR1, and ACVRL1. In sarcoma (N = 166), 8.4% had FOLR1-H and only three genes (NECTIN4, NTHL1 and SLC47A1) were significantly high. Of the 327 colorectal cancers, 8% met the criteria for FOLR1-H and 16 genes were significantly higher in FOLR1-H including NECTIN4, NTHL1, ACVRL1, ROR1/2. In 64 esophageal cancers 10.9% were FOLR1-H, but only 3 genes (GALNT12, ACVRL1 and NECTIN4) were significantly higher. Conclusions: This data suggests that cancers with significantly high expression of FOLR1 mRNA are a special subtype of tumors characterized by the expression of embryonic cell surface markers (FOLR1, TROP2, NECTIN4, ROR1/2). The pan-cancer marked overexpression of these genes suggests that cancers with FOLR1-H represent a subtype of cancers with similar biology. This subtype may benefit from combination therapy targeting more than one of these markers (e.g. anti-FOLR1 with anti-TROP2, or anti-NECTIN4) and clinical trial with such combination may be justified.