BackgroundQuantification of circulating tumor DNA (ctDNA) levels is a reliable prognostic tool in several malignancies. Dynamic changes in ctDNA levels in response to treatment may also provide prognostic information. Here, we explore the value of changes in ctDNA levels in response to immune checkpoint inhibitors (ICIs).MethodsWe searched MEDLINE (host: PubMed) for trials of ICIs in advanced solid tumors in which outcomes were reported based on change in ctDNA levels. ctDNA reduction was defined as reported in individual trials. Typically, this was either >50% reduction or a reduction to undetectable levels. We extracted HRs and related 95% CIs and/or p values comparing ctDNA reduction versus no reduction for progression-free survival (PFS) and/or overall survival (OS). Data were then pooled in a meta-analysis. Variation in effect size was examined using subgroup analyses.ResultsEighteen trials were included in the meta-analysis. ctDNA levels were detectable in all participants in all studies prior to initiation of ICIs. A reduction in ctDNA measured 6–16 weeks after starting treatment was associated with significantly better PFS (HR 0.20; 95% CI, 0.14 to 0.28; p<0.001). Similarly, OS was superior in patients with reduced ctDNA levels (HR 0.18; 95% CI, 0.12 to 0.26; p<0.001). The results were consistent across all disease sites, lines of treatment, magnitude of change (to undetectable vs >50% reduction) and whether treatment exposure comprised single or combination ICIs.ConclusionsIn advanced solid tumors, a reduction in ctDNA levels in response to ICIs is associated with substantial improvements in outcome. ctDNA change is an early response biomarker which may allow for de-escalation of cross-sectional imaging in patients receiving ICIs or support treatment de-escalation strategies.

Background: Multiple anti-PD-1/PD-L1 antibodies have been approved, and in some diseases, there is a choice of more than one. Comparative efficacy, safety and tolerability are unknown. Methods: Randomized trials (RCTs) supporting the registration of single agent anti-PD1 or anti-PDL1 inhibitors between 2015-2019 were identified. We extracted the hazard ratio (HR) for overall survival (OS) and calculated the odds ratio (OR) for commonly reported safety and tolerability outcomes. We then performed a network meta-analysis, reporting multiple pair-wise comparisons between different anti-PD-1/PD-L1 antibodies. Results: Sixteen RCTs comprising 10673 patients were included; 10 in non-small-cell lung cancer, 2 in melanoma, 2 in head and neck squamous cell carcinoma and 2 in urothelial cancer. Compared to pembrolizumab, efficacy was similar for nivolumab (HR: 1.02 95% CI: 0.91-1.14) and for atezolizumab (HR: 0.97 95% CI: 0.85-1.10), however, avelumab appeared inferior (HR: 1.30, 95% CI: 1.06-1.56). Pembrolizumab showed similar odds of serious adverse events (SAEs) as nivolumab (OR: 1.12, 95% CI: 0.56-2.27) and atezolizumab (OR: 1.05, 95%

Disease-free survival (DFS) comprises both breast cancer and non-breast cancer events. DFS has not been validated as a surrogate endpoint for overall survival (OS) in most breast cancer subtypes. We assessed changes to the type of events contributing to DFS over time. We identified adjuvant studies in breast cancer (BC) from 2000 to 2020 where the endpoint was DFS. We examined change in distant DFS events and the BC-related DFS using univariable and multivariable linear regression. Data were reported quantitatively using the Burnand criteria irrespective of statistical significance. We included 84 studies (88 cohorts), comprising 212,191 participants, 41,604 DFS events and 23,205 distant DFS events. The DFS event rate/100 participants/year has declined modestly over time (ß − 0.34, p = 0.001). Start year was negatively associated with distant DFS events (ß − 0.58, p < 0.0001); however, the effect was lost after adjusting for follow-up time (ß − 0.18, p = 0.096). The average number of BC-related events/100 participants/year also declined over time (ß − 0.28, p = 0.009). In multivariable analysis, start year and ER expression were quantitatively associated with distant DFS events and BC-related DFS events. DFS events have declined over time driven by a reduction in BC related events. As DFS events are increasingly defined by non-BC events, there will be limited surrogacy between DFS and OS.

e15151 Background: Multiple ICIs have been approved, and in some diseases there is a choice of more than one ICI. The comparative safety, efficacy, and tolerability are not known. Here we report on a network meta-analysis comparing different ICIs targeting PD1 or PDL1. Methods: Randomized trials (RCTs) supporting the registration of a single agent anti-PD1 or anti-PDL1 inhibitors between 2015-2019 were identified. We extracted the hazard ratio (HR) for overall survival (OS) and calculated the odds ratio (OR) for commonly reported safety and tolerability outcomes. We then performed a network meta-analysis including only disease sites in which more than one ICI has been approved. Multiple pair-wise comparisons were then performed. When more than 2 comparisons were available for a pair of ICIs these were pooled into a single estimate. Analyses were performed in Microsoft Excel and RevMan 5.3. Results: Of 16 RCTs included, 10 in non-small-cell lung cancer, 2 in melanoma, 2 in head and neck squamous cell carcinoma and 2 in urothelial cancer. There was a total of 10673 patients in the analysis. Compared to pembrolizumab, efficacy was similar for nivolumab (HR 1.06, 95% CI 0.97-1.16) and for atezolizumab (HR 1.05, 95% CI 0.93-1.20). However, avelumab appeared inferior (HR 1.29, 95% CI 1.07-1.57). Pembrolizumab showed similar odds of serious adverse events (SAEs) as nivolumab (OR 1.12, 95% CI 0.56-2.27) and atezolizumab (OR 1.05, 95% CI 0.55-2.04). However, compared to nivolumab, atezolizumab was associated with more SAEs (OR 2.14, 95% CI 1.47-3.12). Avelumab had the lowest odds of grade 3-4 adverse events compared to pembrolizumab (OR 0.42, 95% CI 0.24-0.74), nivolumab (OR 0.38, 95% CI 0.24-0.62) and atezolizumab (OR 0.21, 95% CI 0.14-0.33). Atezolizumab was associated with more grade 3-4 adverse events than nivolumab (OR 1.84, 95% CI 1.37-2.47). The odds of treatment discontinuation without progression were similar between nivolumab and atezolizumab (OR 1.20, 95% CI 0.73-2.00), but higher with pembrolizumab compared to nivolumab (OR 1.35, 95% CI 0.83-2.17) and atezolizumab (OR 2.56, 95% CI 1.29-5.00). Pembrolizumab was associated with higher OR of immune related adverse events (IRAEs) compared to nivolumab (OR 2.12, 95% CI 1.49-3.03) and atezolizumab (OR 1.63, 95% CI 1.09-2.43), while the OR of IRAEs was almost similar between nivolumab and atezolizumab. Conclusions: Pembrolizumab, nivolumab, and atezolizumab have similar efficacy. Avelumab appears efficacious. Safety and tolerability seem better with avelumab, but worse with atezolizumab and pembrolizumab.

2544 Background: Quantification of ctDNA levels can be a reliable prognostic tool in several malignancies. More recently, detection of genomic alterations in ctDNA have been validated as a predictive biomarker to guide treatment planning. Dynamic changes in ctDNA levels over time and in response to treatment may also provide prognostic information. However, less is known about the value of changes to ctDNA levels in response to immune checkpoint inhibitors (ICIs). Methods: We searched MEDLINE (host:PubMed) and reviewed trials exploring outcomes of patients with advanced solid tumors receiving ICIs in which outcomes were reported based on changes to ctDNA levels. ctDNA clearance was defined as reported in individual trials. Typically, this was defined as either >50% reduction or a reduction to undetectable levels. We extracted progression free survival (PFS) and/or overall survival (OS) values, related 95% Confidence intervals (CI) and/or p-values. Data were then included in a meta-analysis utilizing the generic inverse variance and random effects model. Variation in effect size was examined using random effects meta-regression analysis. Results: A total of 17 trials were included in the meta-analysis; ctDNA levels were detectable in all participants in all studies prior to initiation of ICIs. Method of detection included next generation sequencing and/or droplet digital polymerase chain reaction assays. Overall, low to undetectable ctDNA levels, measured 6-16 weeks after starting treatment was associated with significantly better PFS, (HR 0.20 95% CI, 0.14-0.28; p<0.001). Similarly, OS was superior in patients with substantially reduced or undetectable ctDNA levels after receiving ICIs, (HR 0.18, 95% CI, 0.12-0.26; p<0.001. The results were consistent across all disease sites, lines of treatment, level of change (undetectable vs. >50% reduction) and whether treatment exposure comprised single or multiple ICIs (see Table). Conclusions: In unselected advanced solid tumors, a substantial fall in ctDNA levels in response to ICIs is associated with substantial improvements in both PFS and OS. ctDNA change is an early response biomarker which may allow for de-escalation of cross-sectional imaging in patients receiving ICIs, or support treatment de-escalation strategies. Further research is needed to quantify variations in sensitivity between the available NGS assays, as well as differences discovery range between assay platforms. [Table: see text]

No abstract

579 Background: The Katherine trial reported a 3-year invasive disease-free survival (DFS) of 77% in patients not achieving pathological complete response (pCR) and continuing on adjuvant trastuzumab. Case series suggest better outcomes and data support that some patients with residual disease have similar outcomes to those with pCR (Steenbruggen et al). The absolute benefit of adjuvant trastuzumab emtansine (T-DM1) would be smaller in patients with favourable outcomes despite residual disease. As such, a more precise estimate of 3-year DFS is needed for treatment planning. Methods: We reviewed reports of randomized trials of neoadjuvant chemotherapy and HER2-directed therapy and extracted the 3-year DFS, a validated surrogate endpoint in HER2-positive early-stage breast cancer. Data were extracted for patients with residual disease and with pCR. The mean 3-year DFS weighted by study sample size was calculated. Meta-regression comprising linear regression weighted by sample size (mixed effects) was performed to explore associations between 3-year DFS and trial-level patient, disease and treatment factors and changes in 3-year DFS over time. Quantitative significance was explored using methods described by Burnand et al. Results: Eleven studies comprising 3908 patients were included in the analysis. The mean 3-year DFS for patients with pCR and for residual disease was 90.1% and 80.0%, respectively. DFS improved over time. For trials whose final year of accrual was after 2010, mean 3-year DFS for residual disease was 84.7% compared to 78.0% for trials completing accrual before that time (p<0.001). In a subgroup analysis of patients with residual disease, those receiving dual HER2-targeted therapy in the neoadjuvant setting had a 3-year DFS of 85.3% compared to 73.3% for those receiving only trastuzumab (p<0.001). Meta-regression results for residual disease are shown in the Table. Positive quantitative significance was observed for final year of accrual, ER-expression, dual anti-HER2 therapy and concurrent vs sequential anti-HER2 therapy. Negative quantitative significance was observed for larger clinical tumor size and nodal involvement. Conclusions: 3-year DFS for patients with residual disease and HER2-targeted therapy is better than reported in the Katherine trial and has improved over time, possibly due to increased use of dual HER2-targeted therapy in the neoadjuvant setting. In this context, the absolute benefit of adjuvant T-DM1 may be smaller than anticipated. [Table: see text]

235 Background: Mutations in BRCA 1/2 are typically associated with breast, ovarian, pancreatic and prostate cancers. BRCA mutations have been reported in colorectal cancer in sporadic case series. Unlike other cancers, the significance of BRCA mutations in mCRC is not known. We report the prevalence and molecular characteristics associated with BRCA 1/2 mutations in mCRC, and investigate the impact of these mutations on chemotherapy response since both oxaliplatin (OX) and irinotecan (IRI) interfere with DNA repair pathways. Methods: The Ontario-wide Cancer Targeted Nucleic Acid Evaluation (OCTANE) database was queried to identify mCRC patients (pts) harbouring BRCA 1/2 mutations. BRCA 1/2 mutations were detected using panel-based next generation sequencing (NGS) on archival tumour tissue. Clinical and molecular variables were collected, together with treatment outcomes. Results: Of 279 mCRC pts within the OCTANE database as of March 2019, 9 pts with BRCA 1/2 mutations were identified (3.2%): 4 BRCA 1 and 5 BRCA 2 mutations. Each patient had a unique variant with 8/9 missense mutations and 1/9 splicing error. Allele frequency ranged from 0.11 to 0.57. RAS or BRAF mutations were present in 67%. Common co-mutations included TP53 (56%), APC (56%), TSC1 (44%), ROS1 (33%) and ATM(33%). 2 pts were mismatch repair deficient. Median age was 48.5 years (range: 31-69 years), 56% males. 5 pts presented with de novo metastatic disease. First line OX-containing chemotherapy was administered to 4 pts, and IRI to 3 pts. 2 pts did not receive chemotherapy (1 had surgery only post-adjuvant OX, and 1 immunotherapy). Overall response rate (ORR) was 71%, with all pts achieving a partial response or stable disease. The median progression-free survival was 7.5 months (range: 1.8- 31.7 months) and median overall survival 68.5 months (range: 10.5- 68.5 months) respectively. Conclusions: BRCA 1/2 mutations are present in a small subset of mCRC pts. Pts with these mutations tend to be younger at diagnosis. BRCA 1/2 mutations are associated with favourable response to first line chemotherapy. Targeting BRCA 1/2 mutations may broaden treatment options for these patients.