Distinguishing endometrial hyperplasia from endometrial adenocarcinoma remains a histopathologic challenge. Several retrospective studies have reported high interobserver variability when assessing the progestin-naive endometrium, while only one study has assessed interobserver variability of postprogestin endometrial biopsies. This study quantified the interobserver variability between trial site pathologists and central pathology review of endometrial specimens taken before treatment with the levonorgestrel intrauterine device (LNG-IUD), 3 months and 6 months post-treatment as part of the feMMe phase 2 randomized clinical trial (NCT01686126). Interobserver agreement was 73% (105/143, κ=0.50) at baseline, 80% (107/134, κ=0.72) at 3 months and 77% (98/127, κ=0.64) at 6 months post-LNG-IUD treatment. Overall, 42% (45/107) site-reported diagnoses of endometrial hyperplasia and 13% (21/161) site-reported diagnoses of endometrial adenocarcinoma were discordant. Site-reported diagnoses were upgraded to higher risk pathology on central review for 77% (72/94) discordant cases. This study confirms the high rate of interobserver variability when diagnosing endometrial hyperplasia or endometrial adenocarcinoma both before and after progestin treatment in specimens collected as part of a clinical trial. It emphasizes the value of confirming diagnosis by a gynecologic pathologist and comparing specimens from the progestin-treated endometrium with the pretreatment biopsy. This study highlights the importance of central pathology review for clinical trial reporting and when deciding on treatment options and assessing response, particularly in the context of progestin treatment.

BACKGROUND:The pathogenesis of female pelvic floor polypropylene mesh complications is unclear, as trials evaluating explanted mesh have not included asymptomatic controls. OBJECTIVE:This study aimed to compare women undergoing ex-plantation of polypropylene mesh with and without complications to determine the pathogenesis of the complications. STUDY DESIGN:Between August 2019 and July 2020, 66 patients who visited the Wesley and Royal Brisbane and Women's Hospital Urogynecology departments with mesh complications and 15 patients who underwent repeat prolapse and/or continence surgery after a previous polypropylene mesh implantation were included. Investigations included 14 histology and immunohistochemical biomarkers and a subgroup of 21 patients who underwent scanning electron microscopy to evaluate degradation and Fourier transform infrared spectroscopy to determine whether any degradation was secondary to oxidation from free radical oxygen species. All scoring was standardized, and reviewers were blinded to group allocation. The mean differences in biomarkers between cases and controls were estimated after accounting for intracluster correlation because of repeated measurements through generalized estimating equation using a linear model framework. The Gwet agreement coefficient was used to assess the consistency in independent reviews, and the Spearman correlation was used to explore biomarker relationships. RESULTS:Cases had significantly increased staining of smooth muscle antigen (suggesting myofibroblasts; mean difference, 0.65; P<.01) and Masson trichome (collagen; mean difference, 0.22; P=.01) and lower levels of foreign body giant cells (mean difference, -0.39; P<.01), blood vessels (mean difference, -0.34; P<.01), CD86 (M1 macrophages; P=.05), and CD4 helper cells (mean difference, -0.58; P<.01) compared with control explants. Cases and controls demonstrated moderate and equal levels of degradation on histology, scanning electron microscopy (P=.86), and oxidation on Fourier transform infrared spectroscopy (P=.01). Degradation correlated poorly with all biomarkers (r<0.04). Persistent and equal levels of CD206 (M2 macrophages), CD68 (total macrophages), CD45 (leucocytes), CD31 (endothelial cells), and CD8 (cytotoxic T Cell) were identified in cases and controls, and the ratio of type I collagen to type III collagen was similar in both groups. Univariate analysis demonstrated that the prolapse mesh was associated with increased foreign body giant cells, CD86 marker, and histologic degradation compared with the continence mesh (P≤.001). Postmenopausal status (P=.04) was independently associated with increased degradation. Smoking status was associated with increased type I collagen deposition (P=.009) and lower foreign body giant cells (P=.03) compared with nonsmoking status. The use of systemic hormone replacement therapy was associated with increased CD31 (P=.01), foreign body giant cells (P=.003), blood vessels (P=.024), and Sirius red staining for type III collagen (P=.001) and decreased CD45 (P=.009) compared with no use of systemic hormone replacement therapy. After duration and mesh type adjustment, foreign body giant cells, blood vessels, CD4, smooth muscle antigen, and Masson trichome remained significant between cases and controls. Multivariate analysis indicated that histologic degradation increased by a score of 0.1/year implantation (P<.01) and was reduced in continence tapes compared with prolapse mesh (mean difference, -0.5 [95% confidence interval, -0.8 to -0.2]). In addition, the duration of implantation was associated with an increased Masson trichome score of 0.02/year, and smooth muscle antigen was increased in cases (mean difference, 0.65 [95% confidence interval, 0.30-1.00]) and explanted prolapse meshes (mean difference, 0.40 [95% confidence interval, 0.02-0.7]) compared with continence tapes. The intraobserver scoring consistency of the Gwet coefficient ranged from fair to very high. CONCLUSION:Oxidation degradation was demonstrated equally in all cases and controls of polypropylene mesh explants. As such we were unable to confirm this was the cause of complications that were related to increased fibrosis and myofibroblast activity possibly secondary to a prolonged inflammatory response.

5604 Background: In the single arm phase 2 PHAEDRA trial, MMR deficiency (dMMR) was predictive of response to durvalumab (1500mg IV Q4W), with an objective tumor response rate (OTR; defined by iRECIST) of 47% in dMMR compared with 3% in MMR-proficient (pMMR) advanced endometrial cancer (AEC). This substudy of the PHAEDRA trial investigates MMR molecular subtypes and other genomic tumor features and their correlation with treatment outcomes. Methods: Testing was performed to determine molecular subtypes of dMMR, including germline pathogenic variants in DNA MMR genes (Lynch syndrome), somatic biallelic MMR gene inactivation through somatic mutation and somatic hypermethylation of the MLH1 gene promoter. DNA from formalin-fixed paraffin-embedded tumor tissue and matched peripheral blood was available from 41/71 (25 dMMR, 16 pMMR) participants for testing on a custom capture-based 298-gene targeted panel (2.005Mb) including the MMR genes and key somatic AEC driver genes. The derived tumor genomic features included microsatellite instability (MSI), tumor mutational burden (TMB), COSMIC v.3.2 tumor mutational signatures and insertion/deletion (Indel) somatic mutation count. Results: Of the 71 patients recruited, 35 were dMMR and 36 were pMMR. Median follow-up was 44 vs 52 months in dMMR vs pMMR participants, respectively. The dMMR molecular subtypes were 4 (11.4%) Lynch syndrome, 4 (11.4%) somatic MMR mutation, 25 (71.4%) MLH1 methylated and 2 (5.7%) dMMR-uncategorised. The OTR rate was 100% (4/4; 95%CI 40-100%) for Lynch, 75% (3/4; 95%CI 22-99%) for somatic MMR mutations and 40% (10/25; 95%CI 22-61%) for MLH1 methylated groups. The median TMB (assessed in 41/71) was higher in those with a confirmed radiological response (37, IQR:26-50) vs non-responders (16, IQR:9-25; p < 0.001). Within the MLH1 methylated group, TMB was also higher in responders vs non-responders (40 v 21; p = 0.03). Somatic mutations in KRAS, PTEN, PIK3CA, ARID1A and TP53 were not associated with OTR rate. Conclusions: dMMR- MLH1 methylated AEC demonstrated greater heterogeneity in OTR to single agent durvalumab than the dMMR-Lynch and dMMR-somatic MMR mutation molecular subtypes. Higher TMB was seen in responders, and specifically within dMMR- MLH1 methylated responders, compared to non-responders. Clinical trial information: ANZGOG1601.

Women with advanced endometrial carcinoma (EC) with mismatch repair (MMR) deficiency have improved outcomes when treated with immune checkpoint inhibitors; however, additional biomarkers are needed to identify women most likely to respond. Scores for programmed death ligand 1 (PD-L1), immunohistochemical staining of tumor (TC+), immune cells (IC+) and presence of tumor-associated immune cells (ICP) on MMR deficient (n = 34) and proficient (n = 33) EC from women treated with durvalumab in the PHAEDRA trial (ANZGOG1601/CTC0144) (trial registration number ACTRN12617000106336, prospectively registered 19 January 2017) are reported and correlated with outcome. Receiver operating characteristic (ROC) analyses and area under the ROC curve were used to determine optimal cutpoints. Performance was compared with median cutpoints and two algorithms; a novel algorithm derived from optimal cutpoints (TC+ ≥ 1 or ICP ≥ 10 or IC+ ≥ 35) and the Ventana urothelial carcinoma (UC) algorithm (either TC+ ≥ 25, ICP > 1 and IC+ ≥ 25 or ICP = 1 and IC+ = 100). The cutpoint ICP ≥ 10 had highest sensitivity (53%) and specificity (82%), being prognostic for progression-free survival (PFS) (p = 0.01), while the optimal cutpoints algorithm was associated with overall survival (p = 0.02); these results were not significant after adjusting for MMR status. The optimal cutpoints algorithm identified non-responders (p = 0.02) with high sensitivity (88%) and negative predictive value (92%), remaining significant after adjustment for MMR. Although MMR status had the strongest association with response, further work to determine the significance of ICP ≥ 10 and the novel optimal cutpoint algorithm is needed.

Endometrial cancer (EC) patients with metastatic/recurrent disease have limited treatment options and poor survival outcomes. Recently, we discovered the FGFR2c splice isoform is associated with poor prognosis in EC patients. Here we report the establishment of 16 EC patient-derived xenografts (PDX)-derived organoids (PDXOs) with or without FGFR2c expression. In vitro treatment of 5 EC PDXOs with BGJ398 showed significant cell death in 3 models with FGFR2c expression. PDXs with high/moderate FGFR2c expression showed significant tumour growth inhibition (TGI) following 21-day treatment with FGFR inhibitors (BGJ398 or pemigatinib) and significantly prolonged survival in 4/5 models. Pemigatinib + cisplatin combination therapy (n = 5) resulted in significant TGI and prolonged survival in one of two p53abn PDXs. All five models treated with cisplatin alone showed de novo resistance and no survival benefit. Seven-day treatment with BGJ398 revealed a significant reduction in angiogenesis and CD206 + M2 macrophages. These data collectively support the evaluation of FGFR inhibitors in a clinical trial.

Abstract Endometrial carcinoma (EC) is the most common gynecological malignancy and fibroblast growth factor receptor 2 (FGFR2) is a frequently dysregulated receptor tyrosine kinase. FGFR2b and FGFR2c are the two main splice isoforms of FGFR2 and are normally localized in epithelial and mesenchymal cells, respectively. Previously, we demonstrated that FGFR2c mRNA expression was associated with aggressive tumor characteristics, shorter progression‐free survival (PFS), and disease‐specific survival (DSS) in endometrioid ECs (EECs). The objectives of this study were to investigate the spatial expression of FGFR2b in normal and hyperplasia with and without atypia of human endometrium and to assess the prognostic significance of FGFR2b expression in EC. FGFR2b and FGFR2c mRNA expression was evaluated in normal (proliferative [n = 10], secretory [n = 15], and atrophic [n = 10] endometrium), hyperplasia with and without atypia (n = 19) as well as two patient cohorts of EC samples (discovery [n = 78] and Vancouver [n = 460]) using isoform‐specific BaseScope RNA in situ hybridization assays. Tumors were categorized based on FGFR2 isoform expression (one, both, or neither) and categories were correlated with clinicopathologic markers, molecular subtypes, and clinical outcomes. The FGFR2b splice isoform was exclusively expressed in the epithelial compartment of normal endometrium and hyperplasia without atypia. We observed FGFR2c expression at the basalis layer of glands in 33% (3/9) of hyperplasia with atypia. In patients with EEC, FGFR2b+/FGFR2c− expression was found in 48% of the discovery cohort and 35% of the validation Vancouver cohort. In univariate analyses, tumors with FGFR2b+/FGFR2c− expression had longer PFS (hazard ratio [HR] 0.265; 95% CI 0.145–0.423; log‐rank p < 0.019) and DSS (HR 0.31; 95% CI 0.149–0.622; log‐rank p < 0.001) compared to tumors with FGFR2b−/FGFR2c+ expression in the large EEC Vancouver cohort. In multivariable Cox regression analyses, tumors with FGFR2b+/FGFR2c− expression were significantly associated with longer DSS (HR 0.37; 95% CI 0.153–0.872; log‐rank p < 0.023) compared to FGFR2b−/FGFR2c+ tumors. In conclusion, FGFR2b+/FGFR2c− expression is associated with favorable clinicopathologic markers and clinical outcomes suggesting that FGFR2b could play a role in tailoring the management of EEC patients in the clinic if these findings are confirmed in an independent cohort.

Women with atypical hyperplasia (AH) or well-differentiated early-stage endometrioid endometrial carcinoma (EEC) who wish to retain fertility and/or with comorbidities precluding surgery, are treated with progestin. Clinically approved predictive biomarkers for progestin therapy remain an unmet need. The objectives of this study were to document the overall response rate (ORR) of levonorgestrel intrauterine device (LNG-IUD) treatment, and determine the association of FGFR2b and FGFR2c expression with treatment outcome. BaseScope RNA ISH assay was utilized to detect expression of FGFR2b and FGFR2c mRNA in the diagnostic biopsies of 89 women (40 AH and 49 EEC) treated with LNG-IUD. Detailed clinical follow-up was available for 69 women which revealed an overall response rate (ORR) of 44% (30/69) with a higher ORR seen in AH (64%) compared to EEC (23%). The recurrence rate in women who initially responded to LNG-IUD was 10/30 (33.3%). RNA ISH was successful in 72 patients and showed FGFR2c expression in 12/72 (16.7%) samples. In the 59 women with detailed clinical follow-up and RNA-ISH data, women with tumours expressing FGFR2c were 5-times more likely to have treatment failure in both univariable (HR 5.08, p < 0.0001) and multivariable (HR 4.5, p < 0.002) Cox regression analyses. In conclusion, FGFR2c expression appears to be strongly associated with progestin treatment failure, albeit the ORR is lower in this cohort than previously reported. Future work to validate these findings in an independent multi-institutional cohort is needed.

Abstract Introduction: Women with atypical hyperplasia (AH) or well-differentiated endometrioid endometrial carcinoma (EEC) who wish to retain fertility and/or with severe comorbidities that preclude surgery, are treated with progestin. Previously, we reported FGFR2c was associated with aggressive tumour behaviour and poor survival outcome in EEC. The purpose of this study was to estimate the response rate of Levonorgestrel IUD treatment and determine the association of FGFR2b and FGFR2c expression with outcome in women with AH/borderline histology (BL) and EEC treated with progestin. Method: BaseScope RNA ISH and immunohistochemistry assays were deployed to detect (FGFR2b and FGFR2c mRNA) and (FGFR2 protein and progesterone receptors), respectively in 89 diagnostic biopsies of patients with AH/BL and EEC treated with progestin. Kaplan Meier Curve and Cox regression model analyses were performed to evaluate the predictive value of FGFR2b and FGFR2c in this cohort. Results: The complete resolution rate (CRR) and overall response rate (ORR) at any time point in the whole cohort were 26/82 (32%) and 35/82 (43%), respectively. When stratified by histologic diagnosis CRR was 47.5% and 17% and ORR 63% and 24% for AH/BL and EEC, respectively. The recurrence rate was 28.7%. FGFR2c expression was documented in 12/72 (15%) cases. Both univariable and multivariable Cox regression analyses showed women with FGFR2c expression were 5-fold more likely to progress compared with FGFR2b positive women (HR 5.4, P<0.0001) and (HR, 5, P<0.001), respectively. Conclusion: Progestin treatment is less effective in patients with EEC. Notably, FGFR2c expression appears to be strongly associated with progestin treatment failure. Citation Format: Asmerom Sengal, Deborah Smith, Rebecca Rogers, Cameron Snell, Elizabeth Williams, Pamela Pollock. FGFR2 isoform switching strongly associates with progestin treatment failure in atypical hyperplasia and well-differentiated endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO033.

Background Endometrial cancer (EC) is a major gynecological cancer with increasing incidence. It comprised of four molecular subtypes with differing etiology, prognoses, and response to chemotherapy. In the future, clinical trials testing new single agents or combination therapies will be targeted to the molecular subtype most likely to respond. Pre-clinical models that faithfully represent the molecular subtypes of EC are urgently needed, we sought to develop and characterize a panel of novel EC patient-derived xenograft (PDX) models. Methods Here, we report whole exome or whole genome sequencing of 11 PDX models and the matched primary tumor. Analysis of multiple PDX lineages and passages was performed to study tumor heterogeneity across lineages and/or passages. Based on recent reports of frequent defects in the homologous recombination (HR) pathway in EC, we assessed mutational signatures and HR deficiency scores and correlated these with in vivo responses to the PARP inhibitor (PARPi) talazoparib in six PDXs representing the different molecular subtypes of EC. Results PDX models were successfully generated from all four molecular subtypes of EC and uterine carcinosarcomas, and they recapitulated morphology and the molecular landscape of primary tumors without major genomic drift. We also observed a wide range of inter-tumor and intra-tumor heterogeneity, well captured by different PDX lineages, which could lead to different treatment responses. An in vivo response to talazoparib was detected in two p53mut models consistent with stable disease, however both lacked the HR deficiency genomic signature. Conclusions EC PDX models represent the four molecular subtypes of disease and can capture intra-tumoral heterogeneity of the original primary tumor. PDXs of the p53mut molecular subtype showed sensitivity to PARPi, however, deeper and more durable responses will likely require combination of PARPi with other agents.

5584 Background: Activity of durvalumab in patients with deficient mismatch repair (dMMR) advanced endometrial carcinoma (EC) was confirmed in the PHAEDRA trial (ANZGOG 1601). This study investigated the association between immune biomarkers and clinical outcomes in PHAEDRA. Methods: Formalin-fixed paraffin embedded sections immunohistochemically stained for PD-L1 using the Ventana platform, were with matched H&E slides scored independently by two pathologists according to the Ventana PD-L1 (SP263) algorithm for urothelial carcinoma (UC). Immune biomarkers assessed were PD-L1 staining of tumor cells (TCP) and immune cells (IC), and presence of tumor-associated immune cells (ICP). Results: Sixty-seven of the 71 patients had sufficient tumor for PD-L1 testing. AUC were 0.667, 0.726 and 0.644 for TCP, ICP and IC, respectively for predicting tumor response. Optimal cutpoints were TCP≥1%, ICP≥10% and IC≥35%. ICP≥10% achieved the highest sensitivity (53%) and specificity (82%) of the individual cutpoints. The optimal cutpoint algorithm was able to identify patients who would not respond, (sensitivity 88%, negative predictive value 92%), but had low specificity (48%) and positive predictive value (37%). Differences in PFS were found using ICP≥10% (logrank p = 0.01), compared to TCP (p = 0.25), IC (p = 0.48) and the UC algorithm (p = 0.08) (Figure 1). PFS was shorter in patients with pMMR than dMMR after adjusting for ICP (HR 2.99, 95%CI: 1.61-5.57, p < 0.001). Adjustment for MMR reduced the prognostic significance of ICP≥10% for PFS (HR 0.59, 95% CI: 0.28-1.23, p = 0.16). For OS, differences were seen for the UC algorithm (p = 0.02), but not ICP (p = 0.07), TCP (p = 0.18) or IC (p = 0.23). Similarly to PFS, adjustment for MMR reduced the prognostic significance of the UC algorithm for OS (HR: 0.53, 95% CI: 0.25-1.12, p = 0.10). Conclusions: In this exploratory analysis, ICP was more closely associated with tumor response and PFS than TCP or IC. ICP alone was better than the UC algorithm for predicting PFS. The optimum cutpoint algorithm was promising for identifying non-responders, but requires external validation. Clinical trial information: ACTRN12617000106336.

Background In this study, we assessed the activity of durvalumab, an antibody to programmed death ligand-1, in two cohorts of women with advanced endometrial cancers (AEC)—mismatch repair proficient (pMMR) and mismatch repair deficient (dMMR). Methods A multicenter phase two study was performed in women with AEC with pMMR tumor progressing after one to three lines of chemotherapy and women with AEC with dMMR tumor progressing after zero to three lines of chemotherapy. Mismatch repair status was based on immunohistochemistry expression. All women received durvalumab 1500 mg given every 4 weeks until progression or unacceptable toxicity. The primary endpoint was objective tumor response by RECIST V.1.1 modified for immune-based therapeutics. Results Seventy-one women were recruited: 35 dMMR and 36 pMMR. Median follow-up was 19 vs 21 months in dMMR versus pMMR, respectively. Median age was 67 years. Histology in dMMR versus pMMR included endometrioid (94% vs 57%) and serous (0% vs 31%) and was high grade in 26% vs 74%. The objective tumor response rate (OTRR) in the dMMR cohort was 47% (17/36, 95% CI 32 to 63), including 6 complete responses and 11 partial responses (PRs)) vs 3% in the pMMR cohort (1/35, 95% CI 1 to 15, PR). In the dMMR cohort, durvalumab was the first-line therapy in 58% (OTRR 57%) and the second-line therapy in 39% (OTRR 38%). Median progression-free survival was 8.3 months in the dMMR cohort vs 1.8 months in the pMMR cohort. The 12-month overall survival (OS) rate was 71% in dMMR vs 51% in pMMR, with median OS not reached for dMMR vs 12 months for pMMR. Immune-related adverse events occurred in 14 women, mostly grades 1–2. Conclusion Durvalumab monotherapy showed promising activity and acceptable safety in AEC with dMMR regardless of prior lines of chemotherapy, but activity was limited in AEC with pMMR. Trial registration numbers ANZGOG1601, ACTRN12617000106336, and NCT03015129.

BACKGROUND:The existing staging systems of uterine leiomyosarcoma (uLMS) cannot classify the patients into four non-overlapping prognostic groups. This study aimed to develop a prediction model to predict the three-year survival status of uLMS.METHODS:In total, 201 patients with uLMS who had been treated between June 1993 and January 2014, were analyzed. Potential prognostic indicators were identified by univariate models followed by multivariate analyses. Prediction models were constructed by binomial regression with 3-year survival status as a binary outcome, and the final model was validated by internal cross-validation.RESULTS:Nine potential parameters, including age, log tumor diameter, log mitotic count, cervical involvement, parametrial involvement, lymph node metastasis, distant metastasis, tumor circumscription and lymphovascular space invasion were identified. 110 patients had complete data to build the prediction models. Age, log tumor diameter, log mitotic count, distant metastasis, and circumscription were significantly correlated with the 3-year survival status. The final model with the lowest Akaike's Information Criterion (117.56) was chosen and the cross validation estimated prediction accuracy was 0.745.CONCLUSION:We developed a prediction model for uLMS based on five readily available clinicopathologic parameters. This might provide a personalized prediction of the 3-year survival status and guide the use of adjuvant therapy, a cancer surveillance program, and future studies.

Abstract Endometrial cancer is a major gynaecological cancer with a high incidence resulting in over 500 Australian women dying every year. Good pre-clinical models are urgently needed to study the biology of this disease, and to develop and test novel treatment strategies. Most current pre-clinical research is conducted in cell lines that often do not resemble the disease on the molecular level and do not recapitulate tumour heterogeneity, which results in untranslatable research findings. Patient-derived xenograft (PDX) models overcome the issues of representing tumour molecular landscape and heterogeneity, making them a translatable pre-clinical cancer model. Here, we generated and genomically characterised 11 PDX models by performing whole genome or whole exome sequencing of primary patient tumours and matched PDX samples. We performed a detailed genomic characterisation of these models to determine their suitability as pre-clinical models, study tumour heterogeneity and identify biomarkers of response and resistance. PDX models were successfully generated from all four molecular subtypes of EC and uterine carcinosarcomas, and they recapitulated morphology and the molecular landscape of primary tumors without major genomic drift. We also observed a wide range of inter-tumor and intra-tumor heterogeneity, well captured by different PDX lineages, which could lead to different treatment responses. An in vivo response to talazoparib was detected in two p53mut models consistent with stable disease, however both lacked the HR deficiency genomic signature. EC PDX models represent the four molecular subtypes of disease and can capture intra-tumoral heterogeneity of the original primary tumor. PDXs of the p53mut molecular subtype showed sensitivity to PARPi, however, deeper and more durable responses will likely require combination of PARPi with other agents. Citation Format: Olga Kondrashova, Vanessa F. Bonazzi, Deborah Smith, Katia Nones, Asmerom Sengal, Robert Ju, Leisl M. Packer, Lambros T Koufariotis, Stephen H. Kazakoff, Aimee L. Davidson, Priya Ramarao-Milne, Vanessa Lakis, Felicity Newell, Rebecca Rogers, Claire Davies, Naven Chetty, Lewis Perrin, John Pearson, Ann-Marie Patch, Andrea Garrett, Nicola Waddell, Pamela Pollock, James Nicklin. Genomic characterization of endometrial cancer patient-derived xenografts reveals intratumor heterogeneity [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PR007.

Approximately 75% of breast cancers express oestrogen receptors (ER), progesterone receptors (PR) or both. Endocrine therapy is a cornerstone of systemic therapy for ER+ breast cancer in both the adjuvant and metastatic setting. Despite adjuvant endocrine therapy, over 20% of women with early-stage disease suffer a relapse which can occur years or decades after diagnosis. ER expression only poorly predicts outcome and better predictive markers of response or resistance are required. Molecular signature assays such as Oncotype Dx, Prosigna, Mammaprint and Endopredict have produced information on prognosis and aid in the decision as to whether patients should have adjuvant chemotherapy in addition to surgery and endocrine therapy. We have recently shown that a physical interaction between ER and PR exists and is potentiated by the presence of oestrogen and progesterone.1 PR alters the interaction between ER and chromatin to change the transcriptional output of the ER complex. We have quantified interactions between ER and PR in breast cancer to demonstrate that low ER/PR interactions are associated with relapse on adjuvant aromatase inhibitors. We are currently utilising a novel patient-derived explant (PDE) culture model to measure the sensitivity of tumours to oestrogen, progesterone, tamoxifen and targeted treatments including CDK4/6 inhibitors. Reference 1. Snell CE, Gough M, Liu C, et al. Improved relapse-free survival on aromatase inhibitors in breast cancer is associated with interaction between oestrogen receptor-alpha andprogesterone receptor-b. Br J Cancer 2018; 119: 1316–25.

Abstract Purpose: Endometrial cancer (EC) is the most frequently diagnosed gynaecological cancer. The majority of women with EC are treated surgically and have a good outcome, however 25-30% of patients presenting with metastases or recurrent disease do not have effective therapies and have <12 months survival. Recent investigations demonstrated radio-chemotherapy has little benefit for women with high-risk EC within the deficient mismatch repair (dMMR) and p53 wild type (p53wt) molecular subtypes. We reported isoform switching from the FGFR2b (epithelial) splice-isoform to the FGFR2c (mesenchymal) splice-isoform in 40% of dMMR and 30% of p53wt ECs. This isoform switching was associated with adverse clinicopathologic markers, shorter recurrence free survival and disease specific survival in the Canadian cohort used to identify and validate the ProMisE molecular risk stratification approach. The objectives of the current study were i) to identify patient derived xenograft (PDX) models with FGFR2c expression and develop PDX derived organoids (PDXOs) for preclinical drug testing, ii) assess the efficacy of the BGJ398 FGFR inhibitor (FGFRi) in FGFR2c expressing models and generate preclinical data that would support an early phase clinical trial in FGFR2c stratified EC patients. Method: BaseScope RNA ISH was used to detect FGFR2c expression in patient tumours, PDX models and PDXOs. PDXOs derived from three independent PDX tumours were established from each of five PDX models (3 showing high FGFR2c expression, 2 showing low/no FGFR2c expression). Each PDXO culture was treated with 300nM BGJ398 (pan-FGFRi) or DMSO for 72 h and assessed using a live-dead assay and confocal microscopy. PDXs from three models were engrafted subcutaneously into 8 weeks female NSG mice and when tumours reached 100-150mm3, mice were randomized (4 mice/arm) and treated with 30mg/Kg BGJ398 or vehicle daily for 21 days. Tumours were measured 3x/week and mice sacrificed when tumours reached 900mm3. Results and conclusion: FGFR2c expression was higher in PDXs representing the dMMR and p53wt subtype compared to p53mut subtype and similar expression levels were seen between patient tumours, PDXs and PDXOs. In vitro FGFRi with BGJ398 showed significant cell death occurred in PDXOs with high FGFR2c expression (p< 0.0001, 2-way ANOVA). These in vitro findings were validated in vivo using PDX68 carrying a FGFR2 C383R mutation and PDX52 and PDX59, both showing FGFR2 isoform switching. Significant tumour growth inhibition and a ~2-fold increase in survival was seen in all three models (PDX68, p<0.0001 and p<0.007; PDX52, p<0.02 and P<0.03; and PDX59 P<0.0001 and P<0.0006 respectively). In conclusion, our investigation revealed FGFRi (BGJ398) was effective in EC PDX models representing both mutational activation and isoform switching of FGFR2. As FGFR isoform switching occurs most commonly in the dMMR subtype where immune checkpoint inhibitors (ICIs) are approved, we propose the combination of ICIs and FGFRi may be more effective in women with FGFR2 activation compared to ICIs alone. Citation Format: Asmerom T Sengal, Vanessa Bonazzi, Olga Kondrashova, Lewis Perrin, Naven Chetty, Deborah Smith, Antonio Gil-Moreno, Eva Colas, Pamela M Pollock. Targeting FGFR2c isoform, a novel therapeutic target with FGFR inhibitor in endometrial cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr LBA020.

Leiomyomas, adenomyosis, and endometriosis are reported to be risk factors for endometrial carcinoma (EC), and adenomyosis and endometriosis also for ovarian carcinoma (OC). We aimed to describe the prevalence of these conditions in EC patients with or without an OC diagnosis, and to investigate their relationship with EC risk and prognostic factors in these patients. We evaluated the co-existence of these three conditions in 1399 EC patients, and compared the prevalence of epidemiological risk factors and tumor prognostic features in patients with each condition versus not. Prevalence of conditions was also assessed in the subset of patients with prior/concurrent OC. The observed coexistence of leiomyomas, adenomyosis and endometriosis significantly deviated from that expected (P = 1.2 × 10−8). Patients were more likely to: report a younger age at menarche (PTrend = 0.004) if they had leiomyomas; have used oral contraceptives (P = 6.6 × 10−5) or had ≥2 full-term pregnancies (PTrend = 2.0 × 10−9) if they had adenomyosis; be diagnosed with EC at younger age (P = 5.0 × 10−11) if they had endometriosis. Patients with prior/concurrent OC were more likely to be diagnosed at younger age (P = 5.0 × 10−5), have endometriosis (P = 9.9 × 10−7), and present with higher stage EC (PTrend = 6.6 × 10−5). These findings justify further consideration of these gynecologic conditions as independent risk and prognostic factors for EC.

Approximately 75% of breast cancers express oestrogen receptors (ER), progesterone receptors (PR) or both. Endocrine therapy is a cornerstone of systemic therapy for ER+ breast cancer in both the adjuvant and metastatic setting. Despite adjuvant endocrine therapy, over 20% of women with early-stage disease suffer a relapse which can occur years or decades after diagnosis. We have recently shown that a physical interaction between ER and PR exists and is potentiated by the presence of oestrogen and progesterone.1 PR alters the interaction between ER and chromatin to change the transcriptional output of the ER complex. We have quantified interactions between ER and PR in breast cancer to demonstrate that low ER/PR interactions are associated with relapse on adjuvant aromatase inhibitors. We are utilising a novel patient-derived explant (PDE) culture model to measure the sensitivity of tumours to oestrogen, progesterone, tamoxifen and targeted treatments including CDK4/6 inhibitors. We are currently recruiting patients to build a library of explanted tumours with functional response data to treatment in PDEs. We will use novel assays including the ER-PR interaction assay, expression data and DNA sequencing to develop new tools to predict treatment response which may be translated into clinical practice. Reference1.Snell CE, Gough M, Liu C, et al. Improved relapse-free survival on aromatase inhibitors in breast cancer is associated with interaction between oestrogen receptor-alpha and progesterone receptor-b. Br J Cancer 2018; 119: 1316–25.

Abstract Purpose: The two most common molecular subtypes of endometrial cancers, mismatch repair deficient (MMRd) and p53 wild-type (p53wt) comprise the majority of endometrial cancers and have intermediate prognoses where additional risk stratification biomarkers are needed. Isoform switching of FGFR2 from FGFR2b to FGFR2c (normally expressed in mesenchymal cells), has been reported in other solid carcinomas. The objective of this study was to investigate the role of FGFR2c in risk stratification of endometrial cancer. Experimental Design: We have developed and optimized a BaseScope RNA ISH assay to detect FGFR2c. FGFR2c expression was determined in a preliminary screening cohort of 78 endometrial cancers and a clinically and molecularly annotated Vancouver cohort (n = 465). Cox regression model analyses were performed to assess the prognostic value of FGFR2c. Results: Univariate and multivariate analyses revealed FGFR2c expression was significantly associated with shorter disease-specific survival (DSS) and progression-free survival (PFS) in endometrioid endometrial cancer (EEC, n = 302). Notably, FGFR2c expression was significantly associated with shorter PFS and DSS in patients with grade 3 EECs (P < 0.003 and P < 0.002) and the European Society Medical Oncology (ESMO) high-risk group (P < 0.0001 and P < 0.002), respectively. Moreover, within the MMRd subtype, FGFR2c expression was significantly associated with shorter PFS (P < 0.048) and DSS (P < 0.001). Conclusions: FGFR2c expression appears an independent prognostic biomarker in patients with EEC and further discerns the outcomes within grade 3 tumors, ESMO high-risk groups, as well as within the MMRd and p53wt subtypes. FGFR2c inclusion into future molecular subtyping can further refine risk stratification of EEC.

Primary malignant melanoma of the uterine cervix is a rare form of mucosal melanoma. It typically has a poor prognosis due to late stage at presentation, aggressive nature and resistance to radiotherapy. Unlike cutaneous malignant melanoma, UV radiation is not an apparent risk factor for tumorigenesis. Furthermore, mucosal melanomas exhibit lower incidences of activating BRAF mutations and higher incidences of KIT mutations compared to their cutaneous counterparts suggestive of divergent aetiologies. We describe a case of a 51 year-old-woman who presented with vaginal bleeding and a cervical mass. Initial biopsy of the cervix and adjacent vaginal mucosa showed an ulcerated malignant tumour with spindled and epithelioid morphology which stained positive for melanoma markers S100, HMB45 and Melan A. The patient underwent a total hysterectomy, bilateral salpingo-oophorectomy and vaginal biopsy sampling where residual malignant melanoma was identified in the cervix with evidence of in-situ melanoma confirming the primary site of origin. Molecular analysis showed no evidence of a BRAF, MEK1, KIT or NRAS mutation. While locoregional control through surgical resection remains the mainstay of treatment, novel advancements in therapies targeting driver oncogenes such as BRAF and KIT, and immune checkpoint inhibitors have shown variable results.