Predictive biomarkers of response to immune checkpoint-based therapies (ICI) remain a critically unmet need in the management of advanced renal cell carcinoma (RCC). The complex interplay of the tumour microenvironment (TME) and the circulating immune response has proven to be challenging to decipher. MicroRNAs have gained increasing attention for their role in post-transcriptional gene expression regulation, particularly because they can have immunomodulatory properties. We evaluated the presence of immune-specific extracellular vesicle (EV) microRNAs in the plasma of patients with metastatic RCC (mRCC) prior to initiation of ICI. We found significantly lower levels of microRNA155-3p (miR155) in responders to ICI, when compared to non-responders. This microRNA has unique immunomodulatory properties, thus providing potential biological rationale for our findings. Our results support further work in exploring microRNAs as potential biomarkers of response to immunotherapy.

e16608 Background: Although available data supports trimodal therapy (TMT) as a bladder sparing treatment for MIBC with outcomes comparable to cystectomy, uptake in Canada is low. A retrospective evaluation in British Columbia, Canada, was undertaken to evaluate real-world outcomes in MIBC patients (pts) undergoing bladder sparing radiotherapy (RT). Methods: MIBC pts were identified from the BC Cancer registry who received RT with curative intent between Jan 1, 2002, and Dec 31, 2020. Disease free survival (DFS), overall survival (OS), and disease specific survival (DSS) were calculated for those receiving RT versus combined modality treatments. Further analysis was undertaken to identify factors associated with outcomes. Results: The population was 231 pts, predominantly male (74%), median age 81 (range: 44-95). Almost all (97%) presented with high-grade MIBC, and 67.1% had an ECOG score of 0-1. The reasons for bladder preservation were frailty/comorbidities (77.1%), pt preference (16%) and inoperability (6.9%). 170 (73.6%) pts underwent RT alone; the remainder were treated with chemoRT (16.5%), neoadjuvant chemotherapy (nCT)+RT alone (5.6%), nCT+chemoRT (3%), chemoRT+adjuvantCT (0.9%), and RT+adjuvantCT (0.4%). The median OS in the RT-only group (25.2 months, 95% CI, 19.5-31) was significantly lower than for chemoRT (39.7 months, 95% CI, 13.5-65.9, p=0.013). Pts who underwent maximal transurethral resection of the bladder tumor (TURBT) in the chemoRT group exhibited significantly prolonged OS (56.5 vs. 31.9 months, p=0.006). Pts with maximal TURBT who had a second TURBT while waiting for RT demonstrated a significant improvement, compared to those with a second TURBT due to submaximal TURBT (59.3 vs. 13.3 months, p<.001). Despite these findings, DSS analysis did not show statistically significant differences between the treatment groups (p=0.38), even when stratified by maximal TURBT (p=0.207). Similarly, the median DFS did not represent a difference between the groups (26.6 vs. 22.2 months, p=0.772). Cox regression analysis revealed the absence of carcinoma in situ trended towards a decreased risk of death (HR: 0.52, p<0.001), as did the absence of hydronephrosis (HR: 0.65, p=0.009) and an increase in the total number of RT fractions (HR: 0.92, p=0.001). In the analysis of treatment modalities (RT vs. chemoRT), there was a significant difference in the distribution of recurrence sites (Chi-Square=4.15, p=0.04). Local recurrences were identified less frequently in the chemoRT group. Conclusions: This population-based study showed notable demographic and treatment-related characteristics that influenced OS, DSS, and DFS. While respecting the limitations of retrospective cohort studies, overall outcomes in this cohort are inferior to those predicted for TMT, but adherence to best practices such as maximal TURBT and combined modality chemoRT result in acceptable long term survival rates.

Primary mediastinal germ cell tumors (PMGCTs) are a rare type of cancer affecting young adults. They have different molecular and clinical features compared to testicular germ cell tumors. Non-seminoma PMGCTs have the shortest 5-year overall survival and the poorest prognosis among all of the germ cell tumor presentations, while seminomas share the same survival and prognosis as their testicular counterparts. There is an unmet need for better treatment options for patients with non-seminoma PMGCTs in both first-line and salvage therapy, as the available options are associated with underwhelming outcomes. Identifying biological and genetic factors to predict treatment responses would be helpful in improving the survival of these patients.

Abstract Predictive biomarkers of response to immune checkpoint-based therapies (ICI) remain a critically unmet need in the management of advanced renal cell carcinoma (RCC). The complex interplay of the tumour microenvironment and components of the circulating immune response has proven to be challenging to decipher. MicroRNAs have gained increasing attention for their role in post-transcriptional gene expression regulation, particularly because they can have immunomodulatory properties. We evaluated the presence of immune-specific exosomal microRNAs in the plasma of patients with metastatic RCC (mRCC) prior to initiation of ICI. We found significantly lower levels of microRNA155-3p (miR155) in responders to ICI, when compared to non-responders. This microRNA has unique immunomodulatory properties, thus providing potential biological rationale for our findings. Our results support further work in exploring microRNAs as potential biomarkers of response to immunotherapy.

5006 Background: Clinical Stage I (CSI) is the most common presentation of germ cell testicular tumors (GCT) and patients are usually managed with active surveillance, in absence of reliable biomarkers of relapse. Circulating plasma miR371a-3p (miR371) has demonstrated high sensitivity and specificity in advanced non teratoma GCT. However, its operating characteristics and power to detect early relapse are still undefined. Methods: CSI GCT patients enrolled in the British Columbia provincial biobank with available plasma samples after radical orchiectomy were included in this study. Plasma miR371 was qualitatively assessed by RT-PCR. Sensitivity, specificity, negative and positive predictive values (NPV, PPV) and AUC in predicting tumor recurrence were evaluated in the post-orchiectomy blood samples and/or during the follow-up prior to or at the time of the clinically evident relapse. Relapse free survival (RFS) was correlated to post-orchiectomy miR371 status. Results: One-hundred-one patients were analyzed, 35 (34.6%) experienced a disease relapse with a median follow-up of 41 months. miR371 was positive in 22/35 of the relapsed patients. The specificity and PPV were 100% (95% CI: 94.5 - 100 for both), sensitivity 62.8% (95% CI: 44.9 - 78.5), NPV 83.5% (95%CI: 76.7 - 88.6) and AUC 0.81 (95% CI: 0.71 - 0.91). No false positive results were observed. The RFS of the patients with positive post-orchiectomy miR37 was significantly shorter (median: 3.5 months vs. not reached; p<0.0001) compared to the patients with a negative post-orchiectomy miR371 (HR: 16.9; 95% CI: 2.1 - 135.7; p<0.0001). miR371 sensitivity correlated with tumor burden, time between tumor relapse and miRNA testing and histology (nonseminoma > seminoma). Conclusions: miR371 has high specificity and PPV in detecting GCT at an early stage and could be used to predict GCT relapse during surveillance and to guide treatment selection after orchiectomy. Further studies have been planned for validation of miR371 clinical utility.

TPS5103 Background: With the discovery of the very promising, germ cell malignancy (GCM) specific, liquid biomarker microRNA 371a-3p (miR371), the investigative trajectory has markedly accelerated. With its outstanding, previously-reported specificity and positive predictive value, miR371 likely will become a powerful tool for clinical decision-making. The primary objective of SWOG S1823/CCTG GCC1 [NCT03067181] is to define the operating characteristics of plasma miR371 expression at the time of clinical relapse for low/moderate risk non-seminoma GCM patients on active surveillance. Methods: S1823 is a prospective, observational, adult GCM translational trial which is actively accruing. Broad eligibility includes all newly diagnosed adult GCM patients. Patients are assigned to low (<25% risk of relapse), moderate (25-90% risk of relapse) or high (≥90% risk of harboring active GCM) risk groups. Pragmatic logistics include using Streck tubes and centralized processing for miR371 sample processing and analytics. Research samples were drawn at the time of routine blood draws minimizing patient burden. Source documents are submitted along with case report forms. This data-gathering model gives an important data quality-control check. S1823 began in July 2020 and has since accelerated its accrual to consistently predicted new enrollments of 20-30 cases/month. As of January 2023, the study enrolled 389 low-risk, 114 moderate-risk and 146 high-risk patients (657 total). Interim analysis is planned at the time 40 non-seminoma GCM patients have relapsed and is anticipated in late 2023 to early 2024. 404 centers have opened S1823. 3 Canadian centers have enrolled >10 patients (range 11-51). 17 USA institutions have enrolled >10 patients (range 11-112). In North America, 9 of the 12-storied GCM clinical research programs have had robust participation. The leading accruing organization was the Kaiser Permanente system where 112 patients have been enrolled. In Canada, all population centers contributed proportionally. In the USA, the dominant enrollment comes from the west coast and mid-west. Proportional enrollments have been seen in Hispanic and Asian populations. The entire study provides rich opportunities for a variety of secondary use and patterns of care projects that will begin to roll out over the next year. Clinical trial information: NCT03067181 . [Table: see text]

407 Background: Active surveillance is routinely recommended to manage patients (pts) with clinical stage I (CSI) germ cell testicular tumors (GCT), the most common presentation of newly diagnosed GCT. Circulating plasma miR371a-3p (miR371) has shown high sensitivity and specificity in pts with metastatic non teratoma GCT or in pts with clinically detectable testicular GCT prior to orchiectomy. However, limited data are available about this biomarker accuracy to detect minimal residual disease post-orchiectomy in pts on active surveillance for early stage disease. Methods: CSI GCT pts with available plasma samples after radical orchiectomy enrolled in the British Columbia provincial biobank research program were selected for this study. RT-PCR was used for qualitative miR371 analysis. Sensitivity, specificity, negative and positive predictive values (NPV, PPV) and AUC in predicting tumor recurrence were evaluated for miR371 and compared to the same operating characteristics of current gold standard diagnostic tests. Relapse free survival (RFS) was correlated to post-orchiectomy miR371 (positive or negative) status. Fisher’s exact test was used to evaluate the sensitivity and specificity, unpaired t-test for comparison of miR371 expression. RFS was calculated using the Kaplan-Meier method, and differences between groups were estimated using the log rank test, 2-sided and with 5% significance threshold. Results: With a median follow-up of 41 months, 101 pts with CSI GTCwere included, of whom 35 (34.6%) experienced a disease relapse during the follow-up. miR371 was positive in 22/35 (62.8%) of the relapsed pts. miR371 positivity preceded clinical evident disease by a median of 3 months (range: 1-12 months).The specificity and PPV were 100% (95% CI: 94.5 - 100 for both), sensitivity 62.8% (95% CI: 44.9 - 78.5), NPV 83.5% (95% CI: 76.7 - 88.6) and AUC 0.81 (95% CI: 0.71 - 0.91). No false positive results were observed. The RFS of the pts with positive post-orchiectomy miR371 was significantly shorter (median: 3.5 months vs. not reached; p<0.0001) compared to the pts with a negative post-orchiectomy miR371 (HR: 16.9; 95% CI: 2.1 - 135.7; p<0.0001). miR371 sensitivity correlated with tumor burden, time between tumor relapse and miRNA testing and histology (nonseminoma > seminoma). Conclusions: miR371 has high specificity and PPV in detecting GCT at an early stage and could be used to guide treatment selection after orchiectomy. Further studies, including the SWOG S1823 clinical trial, are ongoing or have been planned in this setting for validation of clinical utility.

Abstract Background Primary mediastinal nonseminoma germ cell tumors (PMNSGCT) are a subgroup of nonseminoma germ cell tumors (GCT) with poor prognosis. In this study, PMNSGCT-specific genomic landscape was analyzed and correlated with clinical outcomes. Methods DNA was extracted and sequenced from 28 archival tumor tissue of patients with mediastinal GCT (3 seminoma and 25 nonseminoma). Overall survival (OS) and association with gene alterations were estimated using the Kaplan-Meier and univariate Cox regression methods. Results Three patients (11%) had a karyotype XXY, 17/28 (61%) tumor samples presented chromosome 12p amplification. Somatic mutations were detected in 19/28 (68%) samples. The most frequently mutated genes were: TP53 (13/28; 46%), KIT (5/28; 18%), and KRAS (5/28; 18%). Deleterious TP53 alterations were associated with significantly reduced overall survival (HR: 7.16; P = .012). Conclusions TP53 alterations are common in PMNSGCT and are associated with reduced overall survival, potentially underlying the poor sensitivity to chemotherapy observed in these patients.

Background and Objective:Germ cell tumors (GCTs) are uncommon malignancies generally originating from gonads. However, about 5% of GCTs arise outside the gonad (extragonadal), of which 80% develop from the mediastinum. While the prognosis of seminomas is not affected by the gonadal or extragonadal primary location, the prognosis of nonseminoma primary mediastinal GCTs (NS-PMGCTs) is poor, compared to its gonadal counterpart with an estimated 5-year overall survival of about 50%. The current treatments are sub-optimal to increase the cure rate of these rare GCTs. Therefore, molecular insights into these tumors would be valuable to develop novel therapies. The main objective of this review is to describe and dissect the genomic features associated with primary mediastinal GCTs (PMGCTs), highlighting the more frequent genomic alterations and their correlation with clinical outcomes.Methods:We conducted a narrative review of the English literature available in PubMed and Google Scholar between 1982 and 2021, including meta-analyses, systematic reviews, case series and case reports regarding the genomic and clinical features of PMGCTs. We analyzed the available data to describe the molecular characteristics of PMGCTs compared to testicular GCTs (TGCTs), highlighting the most relevant biological and prognostic factors.Key Content and Findings:The high percentage of platinum resistance, the unique association with hematologic malignancies (HMs) and other malignancies, the higher prevalence of P53 mutations, and a distinct genomic landscape characterize this rare disease.Conclusions:Although some studies have unveiled recurrent molecular alterations in PMGCTs, few are particularly suitable for targeted therapy. Due to the rarity of PMGCTs, data sharing and the creation of an international consortium would be helpful to have a better understanding of the molecular drivers of these tumors.