Strickler, John H.

Background: HER2 amplification (HER2+) occurs in approximately 3% of patients with metastatic colorectal cancer (mCRC). Despite the recent addition of HER2-directed therapies to treatment recommendations in the NCCN Guidelines, until more recently there were no FDA-approved treatments. This study examined real-world treatment patterns in patients with HER2+ mCRC in the United States before and after the emerging awareness of HER2-directed therapies in 2018. Methods: This was a retrospective observational study of patients with HER2+ mCRC from the GuardantINFORM database, which contains claims data for patients with Guardant360 genomic testing results. Patients were aged ≥18 years, were diagnosed with mCRC between January 2014 and September 2020, and had confirmed ERBB2 amplification via the blood-based Guardant360 test. Treatment patterns and real-world time to next treatment (rwTTNT) were evaluated. Results: This study included 142 patients with a median age of 59 years; 31 (21.8%) patients with ERBB2 amplifications also had ERBB2 mutations. Treatment patterns were heterogeneous and evolved over time; before 2018, the most common regimen prescribed after detection of ERBB2 amplification was anti-VEGF therapy with or without chemotherapy (31.6%; n=25), and after 2018, HER2-directed therapies were the most commonly prescribed (36.5%; n=23). Median rwTTNT among the overall cohort was 8.4 months (95% CI, 6.5–10.0); rwTTNT was numerically longer in patients who received HER2-directed therapy compared with those who received non–HER2-directed therapies (11.0 months [95% CI, 6.3–12.3] vs 7.2 months [95% CI, 5.8–9.6]). Conclusions: This real-world study of the largest clinically annotated dataset of patients with HER2+ mCRC showed that many patients do not receive HER2-directed therapy despite its inclusion in NCCN Guidelines, with heterogeneous treatment patterns suggesting that standard of care remains undefined and targeted therapy remains underutilized. Greater awareness of the unmet need in this patient population, together with new effective therapies, will facilitate strategies for improved, targeted treatment approaches.

Abstract Background HER2 overexpression/amplification in patients with RAS wild-type (WT) metastatic colorectal cancer (mCRC) may be associated with resistance to standard-of-care anti-EGFR therapies. Given the lack of comprehensive investigations into this association, we assessed the prognostic or predictive effect of HER2 amplification/overexpression on anti-EGFR treatment outcomes. Methods A systematic review of MEDLINE, Embase, and Cochrane Library (2001-2021) identified studies evaluating progression-free survival (PFS), overall response rate (ORR), and overall survival (OS) in HER2-positive vs. HER2-negative patients with RAS WT mCRC who received anti-EGFR treatments and whose HER2 status was known. Meta-analyses of proportions (ORR) and hazard ratios (PFS, OS) were performed using random-effect models with pre-specified sensitivity analyses. Results Five high-quality retrospective cohort studies were included in the meta-analyses representing 594 patients with mCRC. All patients received anti-EGFR treatment, either as monotherapy or in combination with chemotherapy. Meta-analysis of PFS demonstrated a 2.84-fold higher risk of death or progression (95% CI, 1.44-5.60) in patients with HER2-positive (vs. HER2-negative) RAS WT mCRC treated with anti-EGFR regimens. The odds of response to anti-EGFR treatment were 2-fold higher in HER2-negative vs. HER2-positive (odds ratio, 1.96 [95% CI, 1.10-3.48]). Differences in OS were not statistically significant. Sensitivity analyses confirmed the robustness of the base-case estimates. Conclusions While this study could not account for all confounding factors, in patients with RAS WT mCRC who received anti-EGFR therapy, HER2 overexpression/amplification was associated with worse PFS and ORR and may therefore predict poorer outcomes. HER2 testing is important to inform treatment decisions and could optimize outcomes for patients.

3531 Background: Homologous recombination deficient (HRD) colorectal cancer (CRC) has improved overall survival (OS) when exposed to DNA damaging agents (DDA) oxaliplatin (OX) and irinotecan (IR). However, this OS benefit is only observed in HRD mutated CRC. Low expression of wild type (WT) BRCA1 RNA displays prolonged OS in ovarian cancer; this finding has not been investigated in CRC or outside BRCA. We investigate if low expression of WT HR genes is associated with prolonged OS in response to DDA. Methods: A total of 12,860 CRC patients tumor biopsies were analyzed by next-generation sequencing (592, NextSeq; WES, WTS NovaSeq). Patients with HRD mutations and MSI-H were excluded (N = 935). 11,925 patients were included in the analysis. A total of 11 core ( BARD1, BLM, BRCA1, BRCA2, BRIP1, MRE11, NBN, PALB2, RAD50, RAD51, RAD51B) and 7 related ( BAP1, WRN, DNMT3A, ERCC1, FANCA, FANCF, RECQL4) HR genes were analyzed. Samples were classified by RNA expression percentiles within the studied cohort. Real world OS was extracted from insurance claims and calculated using Kaplan-Meier estimates for molecularly defined cohorts from first of OX or IR to last contact. Results: OS benefit is seen in low RNA expression (bottom 10%) compared to high expression (top 10%) of all core WT HR genes except RAD51B, BARD1 and BRCA2 in response to IR. We observe a progressively longer OS with lower associated RNA expression in response to DDA. OS of nearly 7 years was observed in low expressing BRCA1 and RAD51 following IR exposure and 4.5-year OS benefit when compared to high expression of these genes. OS benefit in response to OX was less robust but significantly prolonged in BRCA1 and BRIP1 (Table). Patients harboring HRD mutations had similar OS to WT HR RNA low (bottom 10%) in response to OX (HR = 0.75; p = 0.1) and IR (HR = 0.82; p = 0.36). Conclusions: Here we report a novel subclass of CRC defined as patients with low RNA expressing WT HR genes that exhibit differential sensitivity to DDA. Significantly longer survival is noted in CRC with low expression BRCA1, RAD51 and BLM, while post-OX survival was significantly prolonged with low expression of BRCA1, BRIP1 and FANCA. Further characterization of sensitive HR genes will better predict DDA sensitivity and impact treatment sequencing. [Table: see text]

3528 Background: Tucatinib (TUC) is a highly selective HER2-directed TKI approved by the FDA in combination w/trastuzumab (Tras) for treatment (tx) of pts w/ RAS wild-type HER2+ unresectable or metastatic colorectal cancer (mCRC) that has progressed following tx w/ fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy. There are currently no established best practices for HER2 testing/interpretation in mCRC. Here we present results of central HER2 testing across multiple platforms and response to tx for MOUNTAINEER pts treated w/ TUC + Tras based on central HER2 status. Methods: MOUNTAINEER (NCT03043313) enrolled pts w/ local HER2+ mCRC using ≥1 method: IHC, ISH, and/or NGS testing; retrospective central assessment of HER2 status was performed on multiple platforms. Pts in cohorts A+B were treated w/ TUC + Tras; pts in cohort C were treated w/ TUC monotherapy. Confirmed objective response rates (cORRs) using RECIST v1.1 per BICR, DOR, and PFS were calculated for pts treated w/ TUC + Tras based on each central testing method. Results: 114 pts were enrolled in cohorts A (n = 45), B (n = 39), and C (n = 30) w/ HER2+ tumors per ≥1 local testing method. Of samples submitted for central testing for Cohorts A and B, 70 per IHC/FISH, 50 per tissue NGS, and 71 per blood NGS had evaluable results. In all cohorts, there was 81.0% (95% CI, 68.6-90.1) agreement between blood and tissue NGS, 92.6% (95% CI, 83.7-97.6) between IHC/FISH and tissue NGS, and 79.5% (95% CI, 69.2-87.6) between IHC/FISH and blood NGS. In cohorts A and B, pts w/ HER2+ tumors by central IHC/ISH had a mDOR of 16.4 months (95% CI: 10.6-25.5) and mPFS of 10.1 months (95% CI: 4.2-15.2). cORR was 41.1% to 47.7% for the 3 assays. Detailed HER2 results are presented in the Table. Conclusions: Percent agreement of HER2 status was highest w/ tissue-based platforms. Detection of HER2 amplification by ctNDA NGS is useful; however, pts w/o HER2 amplification should be confirmed w/ a tissue-based assay. HER2 status by all 3 platforms predicted tx response to TUC + Tras. cORR in IHC2+/ISH+ was numerically lower but remained clinically relevant. These data support use of the above methods to identify HER2+ mCRC patients that may benefit from TUC + Tras. Clinical trial information: NCT03043313 . [Table: see text]

TPS3631 Background: The current standard of care (SOC) for the treatment of metastatic colorectal cancer (mCRC) is multi-agent chemotherapy, with or without a VEGF or EGFR inhibitor. Human epidermal growth factor receptor-2 (HER2) is a validated clinical target in breast and gastric cancers. HER2 amplification occurs in 3%–5% of patients with mCRC; the rate of HER2 amplification can increase to approximately 10% in patients with RAS/BRAF wild-type mCRC tumors. Tucatinib (TUC)—a highly selective, HER2-directed tyrosine kinase inhibitor—is approved in multiple regions for HER2-positive (HER2+) metastatic breast cancer, approved in the US for HER2+ metastatic colorectal cancer, and under investigation in gastrointestinal cancers. MOUNTAINEER (NCT03043313) evaluated the safety and efficacy of TUC and trastuzumab (Tras) in patients with treatment-refractory RAS wild-type, HER2+ mCRC. Results from the primary endpoint analysis showed clinically meaningful activity, with a confirmed objective response rate (ORR) per blinded independent central review (BICR) of 38.1% (95% confidence interval [CI] 27.7, 49.3) and median duration of response per BICR of 12.4 months (95% CI 8.5, 20.5). Results also demonstrated TUC + Tras was well tolerated, with a low discontinuation rate (5.8%) and no deaths due to adverse events. MOUNTAINEER-03 will further investigate TUC in combination with modified FOLFOX (mFOLFOX) and Tras in patients with RAS wild-type HER2+ mCRC. Methods: MOUNTAINEER-03 (NCT05253651) is a global, open-label, randomized, phase III study for first-line treatment of HER2+ and RAS wild-type mCRC. Approximately 400 patients will be randomized 1:1 to the TUC experimental arm (TUC [300 mg orally twice daily] + Tras + mFOLFOX) or the SOC arm (mFOLFOX alone or in combination with either bevacizumab or cetuximab). HER2 status is determined centrally with tissue-based HER2 immunohistochemistry and in situ hybridization assays. Eligible patients must not have received prior treatment in the metastatic setting but may have received adjuvant treatment if completed > 6 months prior to enrollment. Patients must be ≥18 years old with an Eastern Cooperative Oncology Group Performance Status of ≤1 and RAS wild-type mCRC. Patients with treated stable central nervous system metastases are eligible. Randomization is stratified by primary tumor location (left-sided vs other) and liver metastases (presence/absence). The primary endpoint is progression-free survival per RECIST v1.1 assessed by BICR. Key secondary endpoints are overall survival and confirmed ORR per RECIST v1.1 assessed by BICR. Enrollment is ongoing in North America, Asia, Australia, and Europe. Clinical trial information: NCT05253651 .

TPS261 Background: Current standard of care (SOC) for treatment (tx) of metastatic colorectal cancer (mCRC) is multi-agent chemotherapy, w/ or w/o a VEGF- or EGFR-inhibitor. HER2 is a validated clinical target in breast and gastric cancers. HER2 amplification occurs in 3%-5% of patients (pts) w/ mCRC; the rate of HER2 amplification can increase to ~10% in pts w/ RAS/BRAF wild-type mCRC tumors. Tucatinib (TUC), a highly selective, HER2-directed tyrosine kinase inhibitor, is approved in multiple regions for HER2+ metastatic breast cancer and is being investigated in gastrointestinal cancers. MOUNTAINEER (NCT03043313) evaluated the safety and efficacy of TUC and trastuzumab (Tras) in pts w/ tx refractory RAS wild-type, HER2+ mCRC. Results from the primary endpoint analysis showed clinically meaningful activity (confirmed ORR of 38.1% and median DOR of 12.4 months) and demonstrated TUC + Tras was well tolerated with a low discontinuation rate (5.8%) and no deaths due to AEs. MOUNTAINEER-03 will further investigate TUC in combo w/ mFOLFOX and Tras in pts w/ RAS wild-type, HER2+ mCRC. Methods: MOUNTAINEER-03 (NCT05253651) is a global, open label, randomized, phase 3 study for 1L tx of HER2+ and RAS wild-type mCRC. Approximately 400 pts will be randomized 1:1 to the TUC experimental arm (TUC [300 mg PO BID] + Tras + mFOLFOX) or the SOC arm (mFOLFOX alone or in combo w/ either bevacizumab or cetuximab). HER2 status is determined centrally w/ tissue based HER2 immunohistochemistry and in situ hybridization assays. Eligible pts must not have received prior tx in the metastatic setting but may have received adjuvant tx if completed > 6 months prior to enrollment. Pts must be ≥18 years of age w/ an ECOG performance status of ≤1 and RAS wild-type mCRC. Pts w/ treated stable central nervous system metastases are eligible. Randomization is stratified by primary tumor location (left-sided vs other) and liver metastases (presence/absence). Primary endpoint is progression-free survival per RECIST v1.1, assessed by blinded independent central review (BICR). Key secondary endpoints are overall survival and confirmed objective response rate per RECIST v1.1 assessed by BICR. Enrollment is ongoing in the US, w/ global sites planned. Clinical trial information: NCT05253651 .

198 Background: HER2 overexpression/amplification (HER2+) occurs in 3%-5% of patients (pts) w/ metastatic colorectal cancer (mCRC). Rates of HER2+ can increase to ~10% in pts w/ RAS/BRAF wild-type mCRC tumors. The MOUNTAINEER trial (NCT03043313) evaluated the efficacy and safety of the investigational combination of tucatinib with trastuzumab in pts with HER2+ and RAS wild-type mCRC. Established regional guidelines for mCRC recommend HER2 testing and HER2-directed treatment options; however, there is currently no established best practice for HER2 testing and interpretation in mCRC. Here, we present data from a concordance analysis comparing breast and gastric HER2 testing algorithms in the mCRC setting. Methods: The MOUNTAINEER trial enrolled pts w/ HER2+ mCRC identified using ≥1 method: tissue-based local immunohistochemistry (IHC), in situ hybridization (ISH), and/or next-generation sequencing (NGS) testing. Archival or fresh tumor tissue was submitted to a sponsor-designated central laboratory for confirmatory HER2 testing w/ IHC/FISH per the package insert of the FDA approved assay and scored by both the breast and gastric algorithms for HER2 IHC. A positive result per the breast scoring criteria for IHC requires circumferential membrane staining for HER2, while the gastric criteria allows for circumferential, basolateral, or lateral staining patterns. Results: A total of 114 pts were enrolled with HER2+ tumors per ≥1 local testing methods; 69 pts were HER2+ by NGS, 46 by IHC 3+, and 36 by ISH. Of 105 pts who had tissue available for central HER2 testing w/IHC/FISH, 98 had valid HER2 results; 82/98 (83.7%) of pts had tumors centrally confirmed as HER2+ using both the breast and gastric algorithms. Tissue samples from pts in the MOUNTAINEER trial had 100% concordance between breast and gastric algorithms in HER2 status and 99% concordance in HER2 IHC score. Conclusions: Central pathology testing using both the breast and gastric criteria showed high concordance between these two commonly used algorithms. A high central confirmation rate of local HER2+ results was also observed. These data support the use of either the breast or gastric algorithms to identify HER2+ mCRC tumors until an FDA-approved HER2 assay is available for mCRC. Clinical trial information: NCT03043313 . [Table: see text]

4086 Background: Abnormalities in the MAPK pathway are potential therapeutic targets in various cancers. However, the clinical impact of alterations in the MAPK pathway in BTC have not been elucidated, especially outside of canonical mutations in KRAS and BRAF. We investigated the clinical outcomes of advanced BTC with MAPK pathway alterations treated with chemotherapy in Japan and the United States. Methods: Patients with advanced BTC who received gemcitabine plus cisplatin as first-line therapy were included from the GOZILA study in Japan and Duke Molecular Registry of Tumors in the US. Genetic abnormalities were detected by Guardant360, a cell-free DNA assay, in Japan and by blood or tissue-based next-generation sequencing (NGS) at Duke University. Two hundred and seven patients with BTC from Japan were included in an exploratory cohort to evaluate the association of MAPK alterations with overall survival (OS) according to MAPK alteration status. One hundred and ten patients with BTC from both Japan and the US harboring oncogenic alterations in the MAPK pathway were included in a biomarker selected cohort to assess the association of specific MAPK alterations with OS. Multivariate analysis was performed using a Cox regression model based on a univariate p-value < 0.2. Results: MAPK pathway-related oncogenic alterations detected in each cohort are shown in the table below. In the exploratory cohort, median OS was shorter for patients with MAPK alterations vs. no MAPK alteration (15.9 m vs. 24.9 m, log-rank p = 0.001). Based on univariate analysis, the following covariates were selected for multivariate analyses: age, prior resection, and MAPK pathway alteration in the exploratory cohort; country, the timing of NGS, distant metastasis, KRAS amplification, and BRAF class 2 mutation in the biomarker selected cohort. In the exploratory cohort, multivariate analysis identified MAPK pathway alterations as an independent predictor of shorter OS with a HR of 1.92 (95% CI = 1.28-2.87, p = 0.001). In the biomarker selected cohort, multivariate analysis identified BRAF class 2 mutations and KRAS amplification as independent predictors of shorter OS with a HR of 16.2 (95% CI = 3.26-80.8, p = 0.001) and 5.97 (95% CI = 1.74-19.3, p = 0.002) respectively. Conclusions: MAPK pathway alterations, especially BRAF class 2 mutation and KRAS amplification, had a significant negative impact on clinical outcomes in BTC receiving first-line chemotherapy. These results are newly confirmed in BTC. [Table: see text]

3571 Background: In colorectal cancer (CRC), mutations in KRAS, NRAS, and BRAF predict resistance to anti-EGFR therapies. In pancreatic ductal adenocarcinoma (PDAC), ~90% of patients harbor KRAS mutations, while KRAS wild-type tumors often have clinically actionable fusion alterations. Thus, in both cancers, the accurate ascertainment of RAS and BRAF driver status is essential. Sequencing of cell-free DNA (cfDNA) from plasma allows convenient assessment of a tumor’s molecular profile, but sensitivity can be limited by low ctDNA shedding. We sought to establish a ctDNA shedding threshold at which actionable driver mutations can be reliably detected. Methods: Molecular reports and matched clinical data were obtained from the Duke Molecular Registry of Tumors and the SCRUM-Japan GOZILA and GI-SCREEN. CRC or PDAC patients with a pathogenic KRAS, NRAS, or BRAF activating point mutation (“driver”) present on tissue next-generation sequencing (NGS) assays and who also had cfDNA assay available were included. Tissue NGS included Foundation One CDx and Oncomine Comprehensive Assay. Guardant 360 (G360) was the sole plasma cfDNA assay. 131 CRC and 24 PDAC cases with 189 total G360 assays met criteria and were included. Samples were analyzed according to detection of the driver mutation and the maximum mutant allele frequency (MAF) of non-driver mutations on G360. An optimal cut-point for max MAF was explored among the CRC and PDAC patients using a maximally selected Wilcoxon rank statistic method. Results: 76.8% of driver mutations were in KRAS, 22.6% in BRAF, and 1.9% in NRAS with an overlap of 1 BRAF and 1 NRAS mutation with a KRAS mutation. Overall sensitivity of G360 for drivers was 83.0% for CRC and 54.2% for PDAC. No variants were detected on G360 in 9.1% of CRC and 37.5% of PDAC. Sensitivity for driver mutations increased with higher maximum non-driver MAF, with MAF > 1% predicting sensitivity > 98% (Table). Optimal cut-point analysis identified MAF of > 0.34% (p < 0.0001), above which the driver was identified in 97% of patients and below which only 27%. Conclusions: In our study, non-driver MAF > 1% on cfDNA NGS predicts high sensitivity for RAS and BRAF mutations and thus is adequate to guide clinical decisions such as anti-EGFR therapy in CRC, evaluation for fusions in PDAC, and validity in clinical trials. MAF ≤0.34% is a clear threshold to consider an assay inadequate and thus seek alternative testing. Sensitivity rises for MAF between 0.35 and 1% but will require greater patient numbers to establish clinically relevant sensitivity thresholds. These results will be updated with additional data for final presentation. [Table: see text]