Targeted Molecular Profiling of Circulating Cell-Free DNA in Patients With Advanced Hepatocellular Carcinoma

PURPOSE

Next-generation sequencing (NGS) of tumor-derived, circulating cell-free DNA (cfDNA) may aid in diagnosis, prognostication, and treatment of patients with hepatocellular carcinoma (HCC). The operating characteristics of cfDNA mutational profiling must be determined before routine clinical implementation.

METHODS

This was a single-center, retrospective study with the primary objective of defining genomic alterations in circulating cfDNA along with plasma-tissue genotype agreement between NGS of matched tumor samples in patients with advanced HCC. cfDNA was analyzed using a clinically validated 129-gene NGS assay; matched tissue-based NGS was analyzed with a US Food and Drug Administration-authorized NGS tumor assay.

RESULTS

Fifty-three plasma samples from 51 patients with histologically confirmed HCC underwent NGS-based cfDNA analysis. Genomic alterations were detected in 92.2% of patients, with the most commonly mutated genes including TERT promoter (57%), TP53 (47%), CTNNB1 (37%), ARID1A (18%), and TSC2 (14%). In total, 37 (73%) patients underwent paired tumor NGS, and concordance was high for mutations observed in patient-matched plasma samples: TERT (83%), TP53 (94%), CTNNB1 (92%), ARID1A (100%), and TSC2 (71%). In 10 (27%) of 37 tumor-plasma samples, alterations were detected by cfDNA analysis that were not detected in the patient-matched tumors. Potentially actionable mutations were identified in 37% of all cases including oncogenic/likely oncogenic alterations in TSC1/2 (18%), BRCA1/2 (8%), and PIK3CA (8%). Higher average variant allele fraction was associated with elevated alpha-fetoprotein, increased tumor volume, and no previous systemic therapy, but did not correlate with overall survival in treatment-naïve patients.

CONCLUSION

Tumor mutation profiling of cfDNA in HCC represents an alternative to tissue-based genomic profiling, given the high degree of tumor-plasma NGS concordance; however, genotyping of both blood and tumor may be required to detect all clinically actionable genomic alterations.

Clinical outcomes for IDH1 mutant biliary tract cancer (BTC) treated with contemporary systemic therapy

513

Background: Isocitrate dehydrogenase 1 and 2 (IDH1/2) play a key role in cellular metabolism and epigenetic regulation. Conserved missense IDH1 mutations lead to an accumulation of the onco-metabolite 2-hydroxygluterate, which drives oncogenesis and inhibits cellular differentiation. Ivosidenib is now approved for IDH1 mutant BTC following the results of the phase III ClarIDHy trial. It remains unclear what are the long-term outcomes for patients (pts) with IDH1 mutant BTC treated with chemotherapy, targeted therapy, and immunotherapy. Methods: This was a retrospective analysis of BTC pts who underwent prospective, clinical grade, next generation sequencing by MSK-IMPACT 341, 410, 468 or 505. The primary objective was to define the clinical outcomes of systemic treatment for those pts with IDH1 mutant BTC. Secondary objectives included description of co-occurring genomic alterations. Progression-free survival (PFS) was calculated from the start date of treatment to the date of progression or death. Overall survival (OS) was calculated from the date of unresectable/metastatic disease. This study was approved by the MSKCC Institutional Review Board (NCT01775072). Results: 1124 pts with BTC underwent somatic genomic sequencing with MSK-IMPACT, 143 (12.7%) of which had IDH1 mutations. 78 (55%) were female and median age at diagnosis was 54 (range 32-94). Almost all were intrahepatic cholangiocarcinoma (139; 97%), with 2 (1.5%) gallbladder, and 2 (1.5%) perihilar. The most common co-occurring alterations were in ARID1A (33; 21.7%), PBRM1 (29;20.3%) and BAP1 (19;13.3%). Median TMB was 2.6 mut/Mb (0.8-68.5). 2 pts had microsatellite instability and 1 had a co-occurring IDH2 mutation. 112 (78%) had unresectable/metastatic disease at diagnosis. The median number of lines of therapy was 2 (0-9). With a median follow up time of 18.4 months (mos) (range 1.5 - 184.2), median OS was 23.8 mos (95% CI 20.4-29.1) for those with unresectable and metastatic disease. When only accounting for pts with distant metastatic disease, median OS was 20.7 mos (95% CI 17.6-28). In those who had first line platinum-based therapy (86/133, 65%), median PFS (mPFS) was 8.3 mos (95% CI 6.4-11.2). 49 (37%) pts were treated with an IDH1 inhibitor, with 46/49 (94%) receiving ivosidenib, 29/49 (59%) in the second line. mPFS for those treated with ivosidenib in second line was 4.6 mos (95% CI 3.6-10.0) vs. 2.6 mos (95% CI 1.8-6.7) for 5-fu based chemotherapy (p=0.032). There was no difference in OS for those treated with IDH1 inhibitors compared to those that were not (25.7 vs. 20.7 mos; p=0.5). 11 (8%) pts received immunotherapy-based treatments with a mPFS of 2.7 mos (95% CI 2.2-NR). Conclusions: Our retrospective data indicate that IDH1 mutant BTC appears to exhibit similar PFS to first-line cytotoxic chemotherapy compared to historic unselected populations with favorable outcomes to second line IDH1 inhibition.

PD-1 Blockade in Mismatch Repair-Deficient, Locally Advanced Rectal Cancer

BACKGROUND

Neoadjuvant chemotherapy and radiation followed by surgical resection of the rectum is a standard treatment for locally advanced rectal cancer. A subset of rectal cancer is caused by a deficiency in mismatch repair. Because mismatch repair-deficient colorectal cancer is responsive to programmed death 1 (PD-1) blockade in the context of metastatic disease, it was hypothesized that checkpoint blockade could be effective in patients with mismatch repair-deficient, locally advanced rectal cancer.

METHODS

We initiated a prospective phase 2 study in which single-agent dostarlimab, an anti-PD-1 monoclonal antibody, was administered every 3 weeks for 6 months in patients with mismatch repair-deficient stage II or III rectal adenocarcinoma. This treatment was to be followed by standard chemoradiotherapy and surgery. Patients who had a clinical complete response after completion of dostarlimab therapy would proceed without chemoradiotherapy and surgery. The primary end points are sustained clinical complete response 12 months after completion of dostarlimab therapy or pathological complete response after completion of dostarlimab therapy with or without chemoradiotherapy and overall response to neoadjuvant dostarlimab therapy with or without chemoradiotherapy.

RESULTS

A total of 12 patients have completed treatment with dostarlimab and have undergone at least 6 months of follow-up. All 12 patients (100%; 95% confidence interval, 74 to 100) had a clinical complete response, with no evidence of tumor on magnetic resonance imaging, 18F-fluorodeoxyglucose-positron-emission tomography, endoscopic evaluation, digital rectal examination, or biopsy. At the time of this report, no patients had received chemoradiotherapy or undergone surgery, and no cases of progression or recurrence had been reported during follow-up (range, 6 to 25 months). No adverse events of grade 3 or higher have been reported.

CONCLUSIONS

Mismatch repair-deficient, locally advanced rectal cancer was highly sensitive to single-agent PD-1 blockade. Longer follow-up is needed to assess the duration of response. (Funded by the Simon and Eve Colin Foundation and others; ClinicalTrials.gov number, NCT04165772.).

Single agent PD-1 blockade as curative-intent treatment in mismatch repair deficient locally advanced rectal cancer

LBA5

Background: Neoadjuvant chemotherapy and radiation followed by surgical resection of the rectum is a standard treatment for locally advanced rectal cancer. A subset of rectal cancer is mismatch repair deficient. Since mismatch repair deficient colorectal cancer is responsive to PD-1 blockade in the metastatic setting, we hypothesized that locally advanced mismatch repair deficient rectal cancer is sensitive to checkpoint blockade and may alter the requirements for chemoradiotherapy and surgery. Methods: We conducted a prospective phase II study in which single agent dostarlimab, an anti PD-1 monoclonal antibody, was administered every 3 weeks for 6 months in patients with mismatch repair deficient stage II and III rectal adenocarcinoma, to be followed by standard chemoradiation and surgery. Patients who achieved a clinical complete response were eligible for omission of chemoradiation and surgery. Results: Twelve patients initiated treatment and have at least 6 months of follow up. All 12 (100%, 95% CI:74%-100%) achieved a clinical complete response with no evidence of tumor on MRI, FDG-PET, endoscopic visualization, digital rectal exam, or biopsy, which satisfied the study’s co-primary endpoint. To date, no patients have required chemoradiation or surgery, and no cases of progression or recurrence have been noted during follow up (range 6-25 months). No serious adverse events > grade 3 were observed. Conclusions: Mismatch repair deficient locally advanced rectal cancer is exceptionally sensitive to single agent PD-1 blockade. Longer follow up is needed to assess response duration. Clinical trial information: NCT04165772.

Next-generation sequencing (NGS) of circulating cell-free DNA (cfDNA) in patients (pts) with advanced hepatocellular carcinoma (HCC)

4110

Background: HCC is often diagnosed based on high-quality cross-sectional imaging, and when a biopsy is pursued, acquisition of tissue may be of limited quantity and quality or complicated by underlying medical comorbidities. NGS of tumor derived circulating cfDNA represents an investigational tool for non-invasive molecular profiling, that has the potential to aid in diagnosis, prognosis, and in monitoring disease status. Although prior reports have evaluated such technologies, few studies have included tumor tissues to confirm histology and to explore plasma-tissue gene concordance. Methods: The primary objective of this retrospective cohort study was to define genomic alterations in circulating cfDNA and to explore plasma-tissue genotype concordance in HCC pts. HCC pts underwent collection of cfDNA for NGS using the MSK-ACCESS 129-gene assay between August 2019 and February 2021. Matched tissue-based NGS with the FDA authorized MSK-IMPACT gene assay was completed when tumor tissue was available. Clinical actionability of sequence variants was annotated by OncoKB, an FDA recognized knowledge base. Clinicopathologic characteristics were extracted, and all data were reported with descriptive statistics. Results: 51 unique patients with 53 plasma samples had an HCC histological diagnosis. Pts were male (39, 76%), median age 69 (42-87), viral hepatitis-related (24, 47%), and advanced stage (Stage III:9, 18%; Stage IV:38, 74.5%). Extrahepatic disease and macrovascular involvement were observed in 28 (55%) and 19 (38%) pts, respectively. 22 (43%) pts had AFP ≥400 ng/mL. 49 (92.5%) of 53 plasma samples had detectable genomic alterations. Median cfDNA yield after extraction was 39.43 ng (range: 7.93-287.68). The most frequently mutated genes occurring in > 10% of patients were TERT (57%), TP53 (47%), CTNNB1 (37%), ARID1A (18%) and TSC2 (14%). The most common oncogenic pathways that contained alterations were WNT-β-Catenin (45%) and PIK3-AKT-TOR (25%). 37 (73%) pts underwent tissue sequencing with MSK-IMPACT with a median time of 9.0 months to the time cfDNA testing. MSK-ACCESS identified mutations observed in tumor in most cases: TERT (20/22; 91%), TP53 (16/17; 94%), CTNNB1 (11/12; 92%), ARID1A (6/6; 100%) and TSC2 (6/7; 86%). In 18 (49%) of 37 paired samples, additional mutations in cfDNA not seen in tumor were detected and included KRAS, EGFR, and TP53 alterations. Potentially actionable mutations were identified through cfDNA in 37% of cases including TSC1/2 (18%), BRCA1/ 2 (8%) and PIK3CA (8%). Conclusions: Circulating cfDNA genotyping with MSK-ACCESS identifies previously reported HCC tumor genomic profiles and revealed tumor-associated mutations in 92.5% of plasma samples. Ongoing efforts will explore predictive and prognostic implications of NGS at different HCC stages as well as kinetics of treatment response.

Immunogenomic characterization of biliary tract cancers: Biomarker enrichment for benefit to immune checkpoint blockade

4083

Background: Several immunomodulatory molecules (PD-L1, B7H4, and CD276) have been associated with biliary tract cancer (BTC) subgroups, suggesting potential value to immune checkpoint blockade (ICB) in this lethal disease. Phase II monotherapy (pembrolizumab or nivolumab), and combination (atezolizumab and cobimetinib) ICB trials reported low response rates in unselected advanced BTC with a wide range of responses. A recent randomized phase III trial (TOPAZ-1) reported an overall survival (OS) benefit among patients (pts) with advanced BTC treated with chemotherapy and anti-PD-L1 ICB. However, no correlation between PD-L1 expression and OS was noted and biomarker enrichment strategy in BTC for immunotherapy remains a key to optimize OS. Methods: From our comprehensive clinico-genomic database for BTC at Memorial Sloan Kettering (MSK), a retrospective genomic landscape and neoantigen analysis was performed using MSK-IMPACT. Potential immunogenic subgroups were evaluated: homologous recombination deficiency (HRD) defined by pathogenic alterations in BRCA1/2, PALB2, and BAP1, microsatellite stability high (MSI-H) defined by MSIsensor score ≥10, and tumor mutation burden (TMB)>10. Clinical outcomes with anti-PD-1 ICB were evaluated. Results: Among N=1,190 pts with BTC, N=1,346 samples were sequenced between 03/2014 and 01/2022. Key actionable alterations included (%): IDH1, 2 (13, 3), FGFR2 fusions (9), ERBB2 amplification (5), BRAF V600E (2), RNF43 (2), POLE (2), NTRK1 fusion (<1). There were N=230 (17%) patients with putatively more immunogenic BTC (iBTC) identified by HRD [ BRCA1/2 (1, 2.4), PALB2 (1), BAP1 (9)], TMB>10, and MSI-H. Frequency, location (intrahepatic, ICC; extrahepatic, ECC; gallbladder, GBC), TMB, and genomic instability score (GIS) are summarized (Table). Among iBTC subgroup, N=32 pts received ICB. Their median follow up was 29.1 months. Median lines of prior therapy was 3. Median PFS was 5.6 M (95%CI: 1.2-10.1) and OS was 33.4 M (23.1-43.6). Conclusion: A subgroup of BTC pts (iBTC) benefit from ICB. Apart from MSI-H and TMB>10, other genomically-defined subgroups such as HRD may benefit from ICB. Prospective studies are needed to evaluate a better biomarker enrichment strategy beyond PD-L1 and TMB, that can represent other immunogenic aspects of tumor neoantigen and microenvironment. [Table: see text]

Nivolumab (NIVO) and drug eluting bead transarterial chemoembolization (deb-TACE): Updated results from an ongoing phase 1 study of patients (pts) with liver limited hepatocellular carcinoma (HCC)

437

Background: TACE is a standard of care for liver limited HCC and impacts the immune microenvironment, potentially augmenting the effects of immune checkpoint inhibitors. Methods: This is a multicenter phase 1 study of NIVO and deb-TACE in unresectable HCC pts and Child Pugh A cirrhosis (NCT03143270). The primary objective is to assess safety. Secondary objectives include response rate by RECIST v1.1, progression-free and overall survival by Kaplan-Meier methodology, and blood/tumor immune correlates. A 3 + 3 design with expansion cohort sequentially evaluates 3 cohorts of differing schedules of NIVO relative to deb-TACE. Deb-TACE (75mg of doxorubicin) is administered on Day 0. NIVO is dosed at 240mg IV every 14 days for 1 year (Cohort 1: NIVO begins day +14 after deb-TACE; Cohort 2, interrupted NIVO dosing begins at Day -28 but is held on the Day 0 then restarted on Day +14; Cohort 3, continuous NIVO dosing begins on Day -28 without interruption). Results: As of September 2021, 19 pts were treated [median 67 years (range: 54-78), male (80%), ECOG PS 0 (47%), Child Pugh A (100%), 3 pts in each cohort 1 and 2, 13 pts in cohort 3]. No cases of treatment related liver failure or Grade 5 adverse events (AEs) were observed. 1 DLT of Grade 3 transaminitis was observed in cohort 3 and resolved without intervention and did not recur with drug rechallenge. Median ALT at baseline, day 28, day 56, and end of treatment (EOT) were 27, 43.5, 36.5, and 29 U/L. Median bilirubin at baseline, day 28, day 56, and EOT were 0.6, 0.6, 0.5, and 0.6 mg/dL. Mean ALBI score at baseline (N=19) and EOT (N=14) were -2.75 ± 0.48 vs. -2.55 ± 0.50. The most common treatment-related AEs of any grade were fatigue (53%), ALT/AST increase (42%), fever (37%), and pruritis (32%). The objective response rate by RECIST v 1.1 was 21% (Table). 5/19 pts remained on study with SD or better for ≥12 (range 12-43) months. Updated survival analysis will be presented at the meeting; correlatives at a separate venue. Conclusions: Nivolumab administered with deb-TACE is safe with antitumor activity. This study provides a needed benchmark for the safety of embolization along with anti-PD1 therapy in liver limited HCC. The clinical question of combining immunotherapy with embolization to improve outcome over embolization alone remains investigational and several, pivotal, phase 3 studies are ongoing. Clinical trial information: NCT03143270. [Table: see text]

PD-1 blockade alone for mismatch repair deficient (dMMR) locally advanced rectal cancer

16

Background: Total neoadjuvant therapy with induction chemotherapy and chemoradiation (chemoRT) is the standard treatment for locally advanced rectal adenocarcinomas. Mismatch repair deficient (dMMR) rectal tumors respond poorly to neoadjuvant chemotherapy. PD-1 blockade is effective in patients with metastatic dMMR colorectal cancers, but its efficacy has not been established in the neoadjuvant setting. The purpose of this study is to evaluate the clinical benefit of neoadjuvant PD-1 blockade in dMMR locally advanced rectal cancer. Methods: We designed a prospective, single-arm, phase II study in which patients with stage II and III dMMR rectal cancer receive neoadjuvant dostarlimab (anti-PD-1) for a total of 6 months. The co-primary objectives are to determine the overall response rate (ORR) and pathologic complete response (pCR) or clinical complete response rate (cCR) with or without chemoRT. Tumor assessment with endoscopic evaluation is performed at baseline, 6 weeks, 3 months and 6 months; imaging is performed at pretreatment baseline, 3 months and 6 months. Patients with cCR by previously established criteria are eligible for non-operative management without chemoRT. Those with residual disease after neoadjuvant dostarlimab receive standard chemoRT. Following chemoRT, any patient failing to achieve a cCR is then managed surgically. Results: A total of 13 patients have been enrolled, with median age 52 years (range 26-78), 77% female, and 92% with node-positive disease by rectal MRI. The ORR is 100% in the 12 patients who have undergone at least a 3-month evaluation. Seven patients have completed induction therapy and all 7 (100%) have achieved a cCR and are undergoing observation without chemoRT or surgery. The rate of progressive disease thus far is 0%. No patients have required chemoRT or surgery. There have been no serious adverse events. Conclusions: Single agent neoadjuvant PD-1 blockade with dostarlimab is effective and well-tolerated in locally advanced dMMR rectal adenocarcinoma and allows patients to avoid chemoradiation and surgery. This suggests a potential new paradigm for treatment of dMMR locally advanced rectal cancer. Follow up and further patient accrual is ongoing. Clinical trial information: NCT04165772.

Alliance/CALGB 80802: Impact of hepatitis C (HCV) on doxorubicin (DO) + sorafenib (S) versus S in patients (pts) with advanced hepatocellular carcinoma (aHCC)

325

Background: Alliance/CALGB 80802 randomized phase III trial evaluated DO+S vs. S in pts with aHCC, and showed no improvement in median OS. Multi-drug resistant pathway mitigation by the Ras/Raf/MEK/ERK pathway and bFGF-mediated activation of Raf-1 promotes the formation of antiapoptotic Raf-1 and ASK1 complex, induced by anthracyclines. S efficiently blocks NS5A-recruited c-Raf mediated HCV replication and viral gene expression. Once inhibited by S, VEGF expression of HepG2 may limit HCV cellular entry. Release of Raf-1-Ask-1 dimer and inhibition of Raf-1 via S putatively differ in the presence or absence of DO. We hypothesize treatment with S reduces HCV titer levels (TL) and influence pts’ outcome. Methods: In 80802 HCV pts, TL were evaluated in both arms at baseline and post-baseline at Day 1 of Cycles 2, 3, and every 2 cycles and at progression or discontinuation of therapy. HCV undetectable (HCV-UN) levels were defined as < 50 copies/mL. TL were evaluated in relation to OS and PFS. HCV RNA levels were measured by TaqMan PCR and by genotype. Results: Of 356 pts, 83 were HCV+ with more Black/African American (25/50 = 50%) vs. White (54/239 = 23%) or other race groups (4/67 = 6%) (p < 0.0001). HCV titer data were available on 54 pts (S: 28, DO+S: 26). At baseline, 12 pts (S: 7, DO+S: 5) were HCV-UN, and post-baseline HCV TL did not significantly differ between treatment arms; one patient in each arm went from detectable (HCV-D) to HCV-UN. Post-baseline, 40 pts were HCV-D vs. 14 who were HCV-UN (S+DO: 8, S: 6 pts). Except for the two pts who became HCV-UN, baseline HCV-D vs. HCV-UN titers was similar to that status post-baseline. PFS and OS between HCV-D and HCV-UN both at baseline and post-baseline are delineated in the table. Conclusions: We observed that S did not influence HCV TL. Pts treated with DO+S vs. S had worse PFS if they had HCV-UN, and further that higher levels of HCV titers at baseline were associated with significantly improved PFS. Given the small sample size, these findings warrant further prospective evaluation. Support: U10CA180821, U10CA180882, U24CA196171; Bayer, Bristol-Myers-Squibb, and Sanofi. https://acknowledgments.alliancefound.org . Clinical trial information: NCT01015833. [Table: see text]

Landscape of DNA-damage-repair/homologous recombination deficiency (DDR/HRD) in hepatopancreaticobiliary (HPB) cancers

4620

Background: Biallelic HR-gene mutations (HRm) confer HRD and sensitivity to DDR-targeted therapies including platinum and PARPi in pancreatic cancer (PDAC). The landscape of DDR/HRD phenotypes in HPB cancers and their clinical implication is yet to be evaluated, the subject of this effort. Methods: Hybrid capture-based comprehensive genomic profiling was performed in a CLIA-certified, CAP-accredited lab (Foundation Medicine, Inc.) on up to 395 genes, including the HR-genes ( BRCA1/2, PALB2, RAD50/51B/C/D, MRE11, ATRX, ATR, ATM, BAP1, BRIP1, CHEK2, NBN, and FANCA). Putative DDR/HRD phenotype was assessed using percent genome under LOH (gLOH) (PMID: 28916367). Variant zygosity was assessed as previously described (PMID: 29415044). From an independent PDAC subgroup among HPB cancers, we evaluated their outcomes on first-line platinum. Results: From a total of 11,174 tumors, pathogenic DDR/HRm were identified in 18% (1980/11174) of HPB cancers, 15% (863/5941) of PDAC, 25% (744/2998) of cholangiocarcinoma, 15% (141/958) of hepatocellular carcinoma, and 17% (152/873) of gallbladder carcinoma. We observed a majority (63%) of DDR/HRm with LOH. Rigorous filtering for tumor purity and copy number quality metrics yielded 34% (4051/11774) cases evaluable. The median gLOH of any biallelic DDR/HRm was 12.9% compared to 8.8% in no DDR/HRm (p=5.7E-33). Strength of the association varied by gene, with the strongest association in BRCA1 (22.3, p=1.5E-10), BRCA2 (20.1, p=1.7E-35), RAD51C (16.7, p=7.8E-4), PALB2 (16.4, p=1.4E-5), BRIP1 (14.3, p=0.02), RAD51B (13.7, p=0.02), and ATM (13.6, p=7.7E-12) (Table). Most other DDR/HR-genes and monoallelic DDR/HRm had weak gLOH. PDAC accounted for 60% of this HPB dataset. In an independent dataset of PDAC at MSK (n=262), biallelic DDR/HRm patients (n=29, 11%) had mostly germline mutations and had significantly improved median PFS on first-line platinum vs. non-platinum (13.3 [95%CI: 9.57-NR] vs 3.8 [95%CI: 2.79-NR] months, p<0.0001). Conclusions: Biallelic DDR/HRm is a distinct population of HPB cancers beyond PDAC and may confer better phenotype in DDR-targeted treatment. Further independent validation is underway. [Table: see text]

A phase II study of induction PD-1 blockade in subjects with locally advanced mismatch repair-deficient rectal adenocarcinoma

TPS4123

Background: The treatment of patients with locally advanced rectal cancer includes total neoadjuvant therapy with chemotherapy, chemoradiation followed by surgery. While most rectal cancers respond to combination induction chemotherapy, patients with mismatch repair deficient (dMMR) or MSI-H tumors have a significantly higher chance of progression with this treatment regimen. dMMR or MSI-H tumors have shown remarkable responses to PD-1 blockade, but the effect of neoadjuvant checkpoint inhibition has not been well studied. In this trial we will determine the pathologic complete response rate (pCR) of neoadjuvant anti-PD-1 blockade followed by standard chemoradiation in dMMR or MSI-H locally advanced rectal cancer. We hypothesize that treatment naïve dMMR or MSI-H rectal cancers will achieve a robust clinical response to PD-1 blockade and that the total neodjuvant therapy with PD-1 blockade followed by chemoradiation will improve pCR rates. Methods: Eligible patients ≥18 years of age with Stage II (T3-4, N-) or Stage III (any T, N+) histologically confirmed dMMR or MSI-H (by NGS) rectal adenocarcinoma will be enrolled. Patients will receive TSR-042 (500mg IV) every 3 weeks for a maximum of 8 cycles (6 months of treatment). Imaging, internal endoscopic exam and ctDNA blood draw will be performed at 6 weeks and every 3 months during induction anti-PD-1 treatment. Adverse events and surgical complications will be graded according to the NCI CTCAE v5 and the Clavien-Dindo classification, respectively. Following neoadjuvant checkpoint blockade, patients will undergo conventional chemoradiotherapy followed by surgical resection. The primary endpoint is pathologic complete response compared with historical control in pMMR patients. Patients will be followed up every 6 months for assessment of disease-free survival for up to five years. Clinical trial information: NCT04165772 .

Nivolumab (NIVO) and drug eluting bead transarterial chemoembolization (deb-TACE): Preliminary results from a phase I study of patients (pts) with liver limited hepatocellular carcinoma (HCC)

525

Background: Regional therapies in HCC impact the immune microenvironment and may augment the effects of immune checkpoint inhibitors. Methods: This is a multicenter phase 1 study of NIVO and deb-TACE in unresectable HCC pts (BCLC Stage B) and Child Pugh A cirrhosis (NCT03143270). The primary objective is to assess safety. Secondary objectives include response rate by RECIST v1.1, progression-free and overall survival by Kaplan-Meier methodology, and blood/tumor immune correlates. A 3 + 3 design sequentially evaluates 3 cohorts of differing schedules of NIVO relative to deb-TACE. Deb-TACE (75mg of doxorubicin) is administered on Day 0. NIVO is dosed at 240mg IV every 14 days for 1 year (Cohort 1: NIVO begins day +14 after deb-TACE; Cohort 2, interrupted NIVO dosing begins at Day -28 but is held on the Day 0 then restarted on Day +14; Cohort 3, continuous NIVO dosing begins on Day -28 without interruption). Results: As of July 2019, 9 pts have been treated [median 65 years (range: 54-76), male (89%), viral (44%;1 HBV, 3 HCV), non-viral (56%;2 EtOH, 1 NASH, 2 unknown), prior resection (44%), prior regional therapy (44%), 3 pts in each cohort]. No cases of treatment related liver failure, dose-limiting toxicity, or Grade 5 adverse events (AEs) were observed. Grade ≥3 AEs possibly related to nivolumab, deb-TACE, or both included: transaminase elevation (1 pt: day 1 post TACE resolved in 7 days without treatment; 2 pts: ≥30 days post TACE resolved with steroids between 20-41 days), post-embolization syndrome (1 pt: resolved in 5 days), asymptomatic lipase increase (1 pt: resolved in 14 days), post-procedural groin hematoma (1 pt: resolved in 2 days). All 9 pts were evaluable for efficacy: 2 (22%) confirmed PR and 7 (78%) SD. 4/9 pts remain on study with SD or better—2 pts continue > 18 months post embolization with durable PRs. 12 months OS rate was 71%. Ongoing correlates will be presented at a separate meeting. Conclusions: Nivolumab given at various times relative to deb-TACE appears safe and tolerable. Cohort 3 continues to accrue to provide a better estimate of safety and antitumor activity of the combination. Clinical trial information: NCT03143270.

Homologous recombination deficiency (HRD): A biomarker for first-line (1L) platinum in advanced pancreatic ductal adenocarcinoma (PDAC)

4132

Background: HRD is an emerging biomarker for platinum therapy in PDAC. The clinical implications regarding differences in outcome between germline and somatic HRD in advanced PDAC treated with 1L platinum is unexplored. Methods: We evaluated overall survival (OS) for advanced PDAC (stage III/IV) based on their pathogenic germline (gHRD) and somatic HRD (sHRD) using integrated genomic profiling from MSK-IMPACT and 1L platinum use. HRD defined by pathogenic alterations from the following genes: BRCA1/2, PALB2, ARID1A/B/2, ATR, ATRX, ATM, BAP1, RAD50/51C/D, BRIP1, NBN, CHECK1/2, FANCA/C, CDK12, and MRE11. Results: Advanced PDAC patients (n=461) treated at MSK enrolled in a prospective database, were evaluated. Median follow-up was 27.6 months (95% CI, 24.6-30.6). Both germline and somatic profilings were available for n=350 (76%) but only somatic profiling was available for n=111 (24%). We identified n=52 patients with gHRD (11.3%), n=42 patients with sHRD (9.1%), and 48 patients with somatic VUS for HRD genes. From all 461 patients, the OS was not different between 1L non-platinum vs. 1L platinum groups (19 M vs. 19.3 M), regardleess of their HRD status. (Table) The OS was superior for gHRD vs. non-gHRD (28.7 M vs. 18.2 M), regardless of 1L treatment choice. However, similar significant OS superiority was neither observed in sHRD vs. non-sHRD, nor in VUS sHRD vs. non-VUS sHRD. In a subgroup analysis of 1L platinum treated patients, the OS was superior in gHRD vs. non-gHRD (NR vs. 17.9 M); however, there was no OS difference between sHRD and non-sHRD. Conclusions: In advanced PDAC patients, only gHRD predicted better overall survival for first-line platinum chemotherapy. These findings emphasize the importance of germline mutation testing of HRD in PDAC. Biomarker validation and functional definition of HRD such as loss of heterozygosity analysis is underway. [Table: see text]

A phase II study of ADI-PEG 20 and FOLFOX6 in patients (pts) with advanced hepatocellular carcinoma (HCC)

TPS477

Background: Arginine depletion interferes with pyrimidine metabolism as well as DNA damage repair pathways, and preclinical data indicate that pairing pegylated arginine deiminase (ADI-PEG 20) with fluoropyrimidines or platinum enhances cytotoxicity in vitro and in vivo in HCC models. A prior phase 1 study of FOLFOX6 and ADI-PEG 20 established the safety and recommended phase 2 dose of the combination in pts with advanced gastrointestinal tumors (Harding et al. CCP 2018). For 23 treatment-refractory HCC pts who were treated at the recommended phase 2 dose on an expansion cohort of the phase 1, the objective response rate (ORR) was 21% (95% CI 7.5-43.7) and median progression-free survival (PFS) was 7.3 months. These data were favorable when compared to historic data for FOLFOX alone where the ORR was ~8% and PFS was 2.93 months and suggest greater clinical activity of the combination (Qin et al. JCO 2013). Prospective confirmation of these results is required. Methods: This is an international, multicenter, single-arm, open-label phase 2 trial of ADI-PEG 20 and FOLFOX6 for advanced HCC pts with Child-Pugh A liver function who progressed on ≥ 2 prior lines of prior systemic therapy (NCT02102022). The primary objective is to define the ORR by RECIST 1.1 as assessed by blinded independent central review. Secondary objectives include determination of safety, disease control rate (DCR), duration of response (DOR), PFS, overall survival (OS), serum arginine, citrulline and anti-ADI-PEG 20 levels over 24 weeks, and alpha-fetoprotein response. Eligible pts receive intravenous FOLFOX6 biweekly at standard doses and ADI-PEG 20 intramuscularly weekly at 36 mg/m.2 Cross-sectional imaging will be completed every 8 weeks until progression of disease. Based on a two-sided exact test of a one-sample proportion with an alpha of 0.05, under a presumed ORR of 22%, there is 80% power to yield 95% confidence interval of 15-26%, which will require 46 objective responses in 225 subjects. Futility will be assessed three times during the study based on having ORR data available for 56, 110, and 166 patients. This Phase 2 will be stopped for futility if the conditional power drops below 20% at any of these time points. Clinical trial information: NCT02102022.