Phase II study of pembrolizumab plus capecitabine and bevacizumab in microsatellite stable (MSS) metastatic colorectal cancer (mCRC)

3565

Background: MSS mCRC rarely responds to pembrolizumab monotherapy, but capecitabine and bevacizumab may induce immune-stimulatory effects. This study evaluates the safety, tolerability and preliminary efficacy of pembrolizumab in combination with capecitabine and bevacizumab in MSS mCRC. Methods: Single-center, phase 2 trial with safety lead-in to confirm the recommended phase 2 dose (RP2D) for capecitabine and expansion cohorts (NCT03396926). Key eligibility: MSS mCRC with stable disease (SD) or progressive disease (PD) on prior fluoropyrimidine-based therapy. Treatment: Capecitabine 1000 mg/m2 PO BID D1-14 Q21 days (confirmed RP2D) plus pembrolizumab 200 mg IV D1 Q21 days and bevacizumab 7.5 mg/kg IV D1 Q21 days. Endpoints: Primary: Objective response rate (ORR) by RECIST 1.1. Key secondary: Safety, duration of response (DOR), progression-free survival (PFS), overall survival (OS). Results: From 04/2018-10/2021, 44 patients (pts) were enrolled. Overall: Median age 53 years (range 28-79); female 50%; Caucasian 61%. Liver metastases at enrollment 80%. Prior therapies: median prior lines of therapy 2 (range 1-5); PD on fluoropyrimidine-containing regimens 91%; prior exposure to bevacizumab 86%. Complete toxicity data are available for 36 off-treatment pts. Grade ≥ 3 treatment-related (tr)AEs occurred in 10 (28%) pts, including grade 3 immune-related AEs in 4 (11%) pts. All-cause serious (s)AEs occurred in 13 (36%) pts and trSAEs in 5 (14%) pts. (tr)AEs leading to dose interruptions, reductions, or delays occurred in 21 (58%) pts, most commonly palmar-plantar erythrodysesthesia syndrome in 17 (47%) pts. Disposition: of 44 pts enrolled, 35 were removed for PD and 1 was removed for treatment noncompliance; 8 treatment ongoing. ORR in 40 evaluable pts was 5% (95% CI: 0.6,16.9). Best response by RECIST 1.1: partial response (PR) in 2 (5%); SD in 26 (65%); PD in 12 (30%). 2 responders: DOR 12 and 15 months, both with liver metastases. Median follow up was 7 months (range 1-45), with median PFS 4.3 months (95% CI: 3.9, 6.1), PFS at 6 months 31.1% (95% CI: 19.2%, 50.4%), and median OS 9.6 months (95% CI: 6.2, 13). Median time on treatment was 5 months (range 1-26). Single cell RNA sequencing on a subset of paired pre- and on-treatment biopsies demonstrated changes in the frequency of dendritic cells. Conclusions: The combination of pembrolizumab with capecitabine and bevacizumab was found to be tolerable with an expected toxicity profile in MSS mCRC pts. The ORR of 5% did not meet the prespecified target of ≥ 15%, however nearly a third of pts had PFS > 6 months. Immune profiling of tumor biopsies and peripheral blood is ongoing. Clinical trial information: NCT03396926.

Pembrolizumab (PEM) plus granulocyte macrophage colony stimulating factor (GM-CSF) in advanced biliary cancers (ABC): Final outcomes of a phase 2 trial

444

Background: Immune checkpoint inhibitors (ICI) have limited activity as monotherapy in unselected patients with ABC; the objective response rate (ORR) of PEM was 5.8% in the multicenter phase 2 KEYNOTE-158 trial. GM-CSF modulates immune cells including monocytes and the innate immune response and has demonstrated safety and prolonged survival (OS) in combination with ipilimumab in melanoma. This phase 2 trial was designed to evaluate the efficacy and safety of PEM in combination with GM-CSF in ABC. Methods: Single-center, phase 2 trial with Simon’s 2-stage design and expansion cohort (EC) (NCT02703714). Key eligibility: ABC with progression/intolerance on ≥ 1 standard therapy, no prior ICI, bilirubin ≤1.5xULN. Treatment: PEM 200 mg IV Q21 days plus 2 cycles of GM-CSF 250 µg SC D1-14 Q21 days in cycles 2 and 3 (Stage 1 and EC) or in cycles 1 and 2 (Stage 2). Primary endpoint was objective response rate (ORR) by RECIST 1.1, H0 5% vs. H1 20%. Key secondary endpoints were safety, progression-free survival (PFS), OS, PD-L1 expression. Exploratory endpoints included relationship between efficacy outcomes and anatomic subsite, risk factors, and tumor genotype. Results: Overall, 42 patients enrolled between 5/2016-12/2019: n = 9 in Stage 1, n = 18 in Stage 2, and n = 15 in EC. Overall: median age 61; female 67%; intrahepatic (ICC) 67%, extrahepatic (ECC) 26%, gallbladder (GBC) 7%; stage IV 90%; hepatitis B/C virus positive (HBV/HCV+) 24%; microsatellite instability (MSI-H)/stable (MSS)/unknown n = 1/35/6. Immune-related (ir)AE occurred in 69%, grade 3/4 treatment-related (tr)AE in 10%, all-cause serious (S)AE in 36%, and trSAE in 7%. ORR was 12% (95% CI: 4, 26), with median PFS of 63 days (95% CI: 55, 125), PFS at 6 months in 27% (95% CI: 14, 43), and median OS 3of 93 days (95% CI: 243, 573). There was no significant difference in ORR, PFS, or OS by anatomic subsite or tumor PD-L1 expression; HBV/HCV+ showed trends toward higher ORR (30% vs 6%, p = 0.08) and longer median PFS (276 vs 63 days, p = 0.06) and OS (1033 vs 323 days, p = 0.052). Conclusions: The combination of PEM plus GM-CSF was safe and well-tolerated with higher ORR than expected for PEM monotherapy in a predominantly MSS ABC population but did not meet target ORR threshold for efficacy. ORR and median PFS and OS were highest in patients with underlying HBV or HCV infection. Immune profiling of on-treatment biopsies and peripheral blood are ongoing to ascertain influence of both PEM and GM-CSF on circulating and tumor immune microenvironment. Clinical trial information: NCT02703714.

Quality of life among colorectal cancer (CRC) survivors participating in a pilot trial of a web-based dietary intervention with text messages

42

Background: Diet may be associated with survival and health-related quality of life (HRQOL) among CRC survivors. Behavioral interventions using web and mobile technology are feasible and acceptable approaches to modify dietary behavior. Little is known about the effect of web-based dietary interventions on HRQOL among CRC survivors. Methods: The Survivor Choices for Eating and Drinking study (SUCCEED) was a pilot randomized wait-list controlled trial designed to determine the feasibility and acceptability of a 12-week (wk) web-based dietary intervention with daily text messages. In this secondary analysis, we estimated the effect of the intervention on HRQOL. Between 2017-2018, 50 CRC survivors were randomized (1:1) to intervention or control. Participants in the intervention arm received the intervention in wk 1-12 and were followed from wks 12-24. Participants assigned to the control arm for 1-12 wks had the option to receive the intervention in wks 13-24. In both arms, HRQOL and sleep quality were assessed using the EORTC QLQ–C30 and CR29 and the Pittsburgh Sleep Quality Index at 0, 12, and 24 wks. Within- and between-group mean changes in HRQOL from enrollment to 12 and 24 wks were evaluated using independent t-test and paired t-test. Results: Follow-up was 88% complete at 12 and 24 wks in the intervention arm and 92% and 80% complete at 12 and 24 wks in controls. Participants mean age was 56 ± 9 y; 34% were men, 70% identified as non-Latinx White, 12% identified as Latinx, and 70% had stage III cancer. Between 0 and 12 wks, an increase in emotional functioning was observed in the intervention arm [mean change: 9.1; 95% confidence interval (CI): 2.2,16.0], while a decrease in emotional functioning was observed in controls (mean change: -5.1; 95%CI: -14.5,4.1; between-group mean difference: 14.3; 95%CI: 3.0,25.6). Between 0 and 24 wks, an increase in social functioning (mean change in intervention: 12.1; 95%CI: 2.1,22.1; between-group mean difference: 13.8; 95%CI: 2.1,25.5) and a decrease in fatigue (mean change in intervention: -9.1; 95%CI: -17.1,-1.1; between-group mean difference: -4.1; 95% CI: -15.8,7.6) was observed in the intervention arm. No other measures of HRQOL or sleep quality differed within or between arms. Conclusions: A web-based dietary intervention with daily text messages may improve emotional and social functioning among CRC survivors. Further study to evaluate the effect of web-based interventions on HRQOL among CRC survivors in larger studies may be merited. Clinical trial information: NCT02965521.

Circulating tumor derived cell-free DNA (ctDNA) to predict recurrence of metastatic colorectal cancer (mCRC) following curative intent surgery or radiation

3565

Background: Over half of patients (pts) with oligometastatic CRC treated with curative intent surgery or radiotherapy experience cancer recurrence with or without adjuvant chemotherapy. ctDNA detection post-definitive treatment could identify high risk pts for additional intervention to eliminate molecular residual disease. Here we report results of a prospective observational study aiming to determine ctDNA detection rates using a sensitive liquid biopsy and to correlate post-procedure ctDNA detection (post-ctDNA (+)) with radiographic mCRC recurrence. Methods: Pts with mCRC intending to undergo a curative intent procedure were prospectively recruited at two US sites. ctDNA was collected pre-procedure, 3 weeks post-procedure, and at multiple structured follow-up timepoints. The presence of ctDNA was evaluated using a plasma-only integrated genomic and epigenomic assay (Guardant Reveal, Guardant Health). A bioinformatic classifier was applied to differentiate tumor derived versus non-tumor derived cell-free DNA. Results: Among 52 enrolled pts, post-ctDNA data is available for 45 pts (87%), with a median of 4 (range 1-10) timepoints per pt. The sample analysis failure rate was 1% (2/217). As of 1/1/2021, the radiographic recurrence rate was 60% with a median follow-up time of 50 (range 4-192) weeks. 23 of 25 pts with post-ctDNA(+) have had recurrence (Positive Predictive Value [PPV], 92%). On average, ctDNA was detected 28 weeks before radiographic recurrence (mean 12 vs. 40 weeks, respectively). The two pts with post-ctDNA(+) but no recurrence have > 3 years follow-up; one pt received adjuvant chemotherapy and cleared ctDNA. With a median event-free follow-up time of 97 (range 4-192) weeks, 4 of 20 pts with no post-ctDNA detection (-) have recurred (Negative Predictive Value, 80%). 3 of 4 pts with recurrence despite post-ctDNA(-) also were pre-ctDNA(-). We observed a sensitivity of 85% and a specificity of 89% for the ctDNA assay. The median time to radiographic recurrence was 36 wks for ctDNA(+) vs. not reached for ctDNA(-) (Hazard Ratio, 7.7; 95% CI, 2.6-22.5; P <.001). Conclusions: In mCRC pts undergoing curative intent surgery or radiotherapy, detection of ctDNA post-procedure had a high PPV for cancer recurrence, with a median lead time of 6 months compared to surveillance imaging. Thus, ctDNA holds promise as a biomarker for pt enrollment on clinical trials and as an endpoint for monitoring of response to experimental therapies in this oligometastatic CRC population.

Characteristics and growth rate of lung metastases in patients with primary gastrointestinal malignancies: A retrospective cohort analysis

442

Background: There are no formal guidelines for the management of GI cancer pts with lung-exclusive or lung-predominant metastases (LM), which generally take a more indolent course than metastatic disease occurring at other anatomic sites. We performed a retrospective analysis at a high-volume tertiary care center to evaluate host and tumor characteristics of this pt population, describe treatment approaches, and model patterns and rates of growth. Methods: Eligible pts were identified through Cancer Center registry data, provider recall, and electronic record review. Criteria included LM occurring either synchronously (SLM) or metachronously (MLM) w/primary cancer diagnosis; nodal, but not visceral or peritoneal, mets allowed. Data re: demographics, tumor characteristics, and rx modalities were collected. We reviewed all eligible CT +/- PET scan reports to gather data on #, location, and size of pulm mets, with all images subsequently reviewed by an independent radiologist. Up to 5 pulm mets were tracked through each pt’s clinical course. Growth rate was estimated using a linear mixed model analysis considering patients as the random. Results: Forty pts were identified between 9/2009 - 12/2019 (23 F/17 M; 28 white/7 Asian/5 other/multi; median age 62 y.o.; n = 15 w/tobacco hx). Tumor types: pancreatic (n = 18), colorectal (n = 12), hepatobiliary (n = 7), other (n = 3). SLM vs MLM:13/27; intact vs resected primary = 16/24. Median time from orig cancer dx to onset of MLM = 16 mos (range, 1 to 60 mos). No. of pulm mets at 1st appearance: 1 (n = 7); 2-5 (n = 17); 6-10 (n = 16). Median size of largest pulm met at 1st appearance = 6 mm (range, 0-39 mm); avg growth rate of largest pulm met = 0.18 mm/month (95% CI, 0.08-0.27). Avg growth rate of up to 5 largest lesions (sum) = 0.35 mm/month (95% CI, 0.07-0.64). Median f/u time prior to rx initiation for MLM = 172 days (range, 25-1547 days); 18 pts developed additional mets during their observation period. Rx modalities for LM: surg (n = 6), radiation (n = 18), systemic rx (n = 32). Addn details specific to cancer type, progression patterns, and pt outcomes will be presented at the meeting. Conclusions: The natural hx of LM varies across the spectrum of GI malignancies. Further larger-scale efforts to define patterns of growth of LM for different GI cancers, informed by size, #, and clinical/molecular features, are needed to guide appropriate timing and selection of rx as well as surveillance strategies.

Phase II study of pembrolizumab plus capecitabine and bevacizumab in microsatellite stable (MSS) metastatic colorectal cancer (mCRC): Interim analysis

77

Background: MSS mCRC rarely responds to pembrolizumab monotherapy, but capecitabine and bevacizumab may induce immune-stimulatory effects. This study evaluates the safety, tolerability and preliminary efficacy of pembrolizumab in combination with capecitabine and bevacizumab in MSS mCRC. We present results at the planned interim analysis. Methods: Design:single-arm, open-label, single-site phase 2 trial with a safety lead-in to confirm the recommended phase 2 dose (RP2D) for capecitabine and expansion cohorts. Per the Simon’s 2-stage design, ≤1 response in 29 patients (pts) requires trial suspension. Key eligibility criteria: MSS mCRC with stable disease (SD) or progressive disease (PD) on prior fluoropyrimidine-based therapy. Treatment: RP2D PO capecitabine on days 1-14 plus 200 mg IV pembrolizumab and 7.5 mg/kg IV bevacizumab on day 1 in 21-day cycles. Pts are followed for toxicity and radiographic response. Results: From 04/2018-09/2020, 29 pts were enrolled, of whom 15 (52%) were female; 21 (72%) white; and median age was 55 years (range 36-77 years). Prior therapies: 2 (7%) pts had SD and 27 (93%) pts had PD on fluoropyrimidine-containing regimens; 24 (83%) pts had prior exposure to bevacizumab. The RP2D for capecitabine was 1000 mg/m2 PO BID, with no dose limiting toxicities observed. Complete toxicity data are available for 25 off-treatment pts. The most common related adverse events (AEs) were palmar-plantar erythrodysesthesia (PPE) (64%) and fatigue (68%). Grade ≥3 related AEs occurred in 9 (36%) pts, including immune-related AEs of Grade 3 dyspnea, hypophosphatemia, and pancreatitis in 1 pt each. Treatment related AEs leading to dose interruptions, reductions, or delays occurred in 15 (60%) pts, most commonly PPE in 13 (52%) pts. No pt had a related AE leading to treatment discontinuation or death. Disposition: of 29 pts enrolled, 24 were removed for PD and 1 was removed for an unrelated AE. Best response by RECIST 1.1 in 23 evaluable pts: partial response (PR) in 2 (9%); SD in 14 (61%); PD in 7 (30%). Median time on treatment was 6 months (range 2-26 months). Conclusions: Combination of pembrolizumab with capecitabine and bevacizumab was found to be tolerable with an expected toxicity profile in MSS mCRC pts. With 2 responses, the study met interim analysis criteria to continue accrual. Tissue and blood-based immune correlatives are planned. Clinical trial information: NCT03396926.

Phase I prospective trial of TAS-102 (trifluride and tipiracil) and radioembolization with 90Y resin microspheres for chemo-refractory colorectal liver metastases

110

Background: Clinical efficacy of Yttrium-90 (90Y) radioembolization (TARE) for patients with chemotherapy-refractory metastatic colorectal cancer (mCRC) is limited by extrahepatic disease progression. TAS-102 (trifluride and tipiracil) has overall survival benefit for patients with refractory mCRC and may be a radiosensitizer. We aimed to evaluate the safety of the combination of TAS-102 and 90Y resin TARE in a Phase I dose-escalation trial. Methods: Adult patients with bilobar liver-dominant chemo-refractory mCRC were treated with sequential Y90 resin TARE (body surface area dosimetry) in combination with TAS-102 (20mg/m2, 27mg/m2, and 35mg/m2) in 28-day cycles according to 3+3 dose-escalation design. Beginning with cycle 3, TAS-102 was administered as monotherapy until disease progression or development of intolerable toxicity. Primary objectives were to determine maximum tolerated dose (MTD) of TAS-102, to assess toxicity, and to establish safety of TAS-102 in combination with 90Y TARE. Results: A total of 14 patients (10 women, 4 men) have been treated to date. Among 9 patients enrolled in the dose-escalation phase, no dose limiting toxicities were observed. The MTD of TAS-102 in combination with Y90 was 35mg/m2, which was selected for the dose expansion phase. Severe adverse events (AEs) included: neutropenia (46%); anemia (23%); and thrombocytopenia (8%), which were attributed to TAS-102. All other AEs were mild and transient. At least one follow-up imaging study has been obtained for 13 patients, and 10 patients have completed trial participation. Disease control rate in the liver was 100%. Conclusions: The combination of TAS-102 and 90Y TARE for patients with liver-dominant mCRC is safe and consistently achieved disease control within the liver. Severity and incidence of AEs is within the expected range of TAS-102 and 90Y TARE monotherapy. A dose-expansion phase with planned enrollment of 12 patients is ongoing. Clinical trial information: NCT02602327.

Molecular characterization of a gastric cancer transmitted from an organ donor to four transplant recipients

414

Background: Donor-derived malignancy may occur even when not suspected based on donor or recipient factors, including age and time to cancer diagnosis. Early recognition of donor-derived malignancy has treatment implications. We describe the molecular characterization of a gastric cancer transmitted from an organ donor to heart, liver (LR), left kidney (LKR), and right kidney-pancreas (KPR) recipients. Methods: IRB approval for chart review was obtained; LR, LKR, and KPR also provided research consent for molecular profiling. Short Tandem Repeat (STR) genotyping was performed by polymerase chain reaction and gel electrophoresis. Tumor and germline DNA from patients and the organ donor were subjected to next generation sequencing (NGS) of 479 genes. Fluorescence in situ hybridization (FISH) was used to confirm MET amplification. Results: Donor origin was established by STR analysis, with the tumors showing high levels of donor alleles. Pathology revealed a poorly differentiated adenocarcinoma with signet ring features. Immunohistochemical staining and CA-19-9 elevation were most consistent with gastric or pancreas origin. Tumor sequencing was notable for somatic mutation of CDH1, MET amplification and wild-type KRAS genes. Tumors from LR and KPR were nearly identical based on pathogenic variants, allele frequency, and copy number variation. Insufficient tumor cellularity in all LKR specimens precluded NGS profiling, but clinical testing found that the cancer was mismatch repair proficient; ERBB2 equivocal; and PDL-1 positive. A circulating tumor DNA test did not uncover any genomic alterations; however, MET amplification was confirmed in this tumor using FISH probes. Conclusions: STR analysis and reporting should be standard immediately following diagnosis of cancer in an organ transplant recipient to ascertain donor derivation. Further molecular characterization, including NGS, may aid in defining primary tumor origin. Here, diagnosis with PDL1-positive gastric cancer enabled use of pembrolizumab. One patient remains alive and without evidence of cancer following prompt organ explant after cancer was reported in other recipients.

Factors affecting differential outcomes in the definitive treatment of anal cancer between HIV+ and HIV- patients

3572

Background: Anal cancer is an uncommon malignancy with numerous factors that influence treatment outcomes. Historically, HIV+ patients were restricted from entering clinical trials, limiting data on their outcomes to small retrospective reports. This study seeks to understand the factors related to anal cancer outcomes, specifically the differences between HIV+ and HIV- patients. Methods: Inclusion criteria was non-metastatic anal squamous cell carcinoma treated with a definitive course of chemotherapy and radiation between 2005 and 2018 at a single institution. Clinical data related to baseline characteristics, treatment parameters, and post-treatment follow-up were extracted for calculation of freedom from local recurrence (FFLR) and overall survival (OS). Univariate analysis (UVA) and multivariate analysis (MVA) were done using cox proportional hazard model, and FFLR and OS were calculated using the Kaplan-Meier method. Results: During the study period, 111 patient initiated definitive treatment for anal cancer. Median age was 56.7 years (IQR: 51.4-63.5), and 47% (N = 52) were HIV+. At median follow-up of 28 months, 12 and 24-month FFLR was 84.1% and 78.2% respectively, with 24-month OS of 87.3%. MVA demonstrated significant association between FFLR and T-stage HR 4.02 (95% CI: 2.14-7.55) p < 0.001, elapsed treatment time (median of 50 days) 1.08 (95% CI: 1.04-1.12) p < 0.001, and diagnosis to treatment start (median time of 15 weeks) 1.05 (95% CI: 1.01-1.08) p = 0.005. Additional analysis with log-rank test for FFLR demonstrated significant difference between patients taking < 50 days to complete treatment (p = 0.03), and < 15 weeks from diagnosis to treatment completion (p = 0.006). In HIV+ patients, post-treatment CD4 < 150 was significantly associated with worse OS on log-rank test (p = 0.016), with pretreatment CD4 values being non-significant. Conclusions: This study represents the largest single institution report of HIV positive patients treated for anal cancer. No difference in local recurrence or overall survival between HIV+ and HIV- patients was elucidated; however, HIV+ patients with lower post-treatment CD4 counts had worse OS. The most significant predictors of local recurrence were advanced T-stage, increased time from diagnosis to treatment initiation, and prolonged treatment time.

Circulating tumor derived cell-free DNA (ctDNA) to predict recurrence of metastatic colorectal cancer (mCRC) following curative intent surgery or radiation: Interim results

552

Background: Over half of patients (pts) with oligometastatic CRC treated with definitive surgery or radiotherapy experience cancer recurrence. Early detection of ctDNA could identify high risk pts for additional intervention to eliminate micrometastatic disease. Here we report interim results of a prospective study aiming to determine ctDNA detection rates using a sensitive multigene assay and to correlate post-procedure ctDNA detection with radiographic mCRC recurrence. Methods: Pts with mCRC intending to undergo a curative intent procedure were prospectively recruited at a single site. ctDNA was collected pre-procedure, 3 weeks (wks) post-procedure, and at multiple follow-up timepoints. ctDNA detection utilizing a multi-gene sequencing panel (Guardant Health) included somatic variant and epigenetic assessments. A novel variant classifier was applied to differentiate tumor derived versus non-tumor derived alterations. A Simon’s two-stage design with planned interim analysis to assess 3wk post-procedure ctDNA detection rate was employed. Results: Of 25 pts enrolled, 21 (84%) had evaluable paired pre- and post-procedure samples. In these 21 pts, the 3 wks post-procedure sample was collected after surgery (N = 20) or radiation (N = 1) to address liver (N = 17), lung (N = 3), or ovarian (N = 1) metastases ± colon resection (N = 6). ctDNA was detected (+) in 15/21 (71%) pre- and 11/21 (52%) post-procedure samples. ctDNA was (+) in 8/12 (67%) pre- and 8/17 (47%) post-procedure samples with carcinoembryonic antigen < 5 ng/ml. Conclusions: In this interim analysis of pts with mCRC undergoing curative intent procedures, the post-procedure ctDNA detection rate was 52%. The similarity between the observed post-procedure ctDNA detection and expected recurrence rate suggests promise for recurrence prediction using this approach. Given post-procedure ctDNA was (+) in > 3 pts, the study will continue to enroll, and pts are being followed for future correlation of ctDNA with radiographic recurrence. [Table: see text]

Lifestyle and outcomes after gastrointestinal cancer: A prospective cohort study (LOGIC)

180

Background: The number of individuals living after a diagnosis of gastrointestinal (GI) cancer is increasing. Emerging data suggest modifiable lifestyle factors impact survival after colorectal cancer (CRC), however very little is known about survivorship in other GI cancers. Given the common thread of multimodality therapy among many GI cancer survivors, there is a paucity of data on sexual function, fertility, anxiety/depression, changes in comorbidities, and quality of life after cancer treatment. Additionally, existing cohort studies of GI survivors are primarily European, and further data are needed from survivor populations in the US . Methods: Patients of the University of California, San Francisco GI Oncology Survivorship Clinic who are designated disease-free are recruited by mail or in clinic. We send secure online questionnaires to participants every six months for five years and annually thereafter. At varying intervals, questionnaires solicit sociodemographics, diet, physical activity, fertility, medical and smoking history, fear of cancer recurrence, sexual health, quality of life, psychological well-being, and sleep quality. Pathoclinical disease characteristics, treatment, and recurrence status are abstracted from the medical record at baseline and updated annually. Results: Between February and August 2017, 111 patients were enrolled; 68% of participants completed ≥1 and 57% completed all baseline questionnaires. Most patients had a history of colon cancer (52%, n = 58) or rectal cancer (31%, n = 34). Other diseases include: anal cancer (12%, n = 13), gastrointestinal stromal tumor (3%, n = 3), and other GI cancers (3%, n = 3). Fifty-eight percent of patients were female, 76% identified as white and median age at diagnosis was 55 (range 20-81). Median time from initial GI cancer diagnosis to study entry was 27 months. Following the initial recruitment wave of established patients, the average rate of enrollment is ~3 patients/week. Conclusions: Results from this ongoing cohort study will improve our understanding of modifiable risk factors for GI cancer recurrence and key survivorship issues related to psychological well-being, sexual function, fertility management, and quality of life.

Phase II trial of pembrolizumab (PEM) plus granulocyte macrophage colony stimulating factor (GM-CSF) in advanced biliary cancers (ABC)

386

Background: The efficacy of immune checkpoint inhibition (CPI) has not been established in ABC. GM-CSF modulates immune effector cells and has demonstrated safety and improved survival (OS) in combination with ipilimumab in melanoma. This phase 2 trial aims to evaluate the efficacy and safety of PEM in combination with GM-CSF in ABC. Methods: Design: Simon’s 2-stage. Key eligibility: ABC with progression/intolerance on ≥ 1 standard therapy, no prior CPI, bilirubin ≤1.5xULN. Treatment: PEM 200 mg IV Q21 days plus 2 cycles of GM-CSF 250 µg SC D1-14 Q21 days in cycles 2 and 3 (Stage 1 Safety Cohort) or in cycles 1 and 2 (Stage 2). Endpoints: 1◦: Progression-free survival at 6 months (PFS6) with H0 25% vs. H1 50%. Key 2◦: Safety, overall response rate (ORR) and duration (DOR), OS, PD-L1 expression. Exploratory: PBMC and tumor immune cell profiles, tumor genotype, microsatellite (in)stability (MSI or MSS). Results: Accrual has completed with 27 patients (pts) enrolled 5/2016-6/2017: F/M 13/14; median age 61 (range 37-77); intrahepatic 19 (70%), extrahepatic 7 (26%), mixed 1 (4%) cholangiocarcinoma; stage IVA/B 85%, II/III 15%; median prior therapies 2 (range 1-6). Adverse events (AE): Related grade(Gr) ≥3 AE occurred in 4/27 (15%) pts including immune-related (ir)AE of Gr4 diabetes mellitus and Gr3 thrombocytopenia in 1 pt each. Gr≤2 irAE in ≥5% were: arthralgia (33%), dry eye/mouth (15%), hyperthyroid/thyroiditis (15%), hypothyroid (15%), neuropathy (11%), rash (11%), and adrenal insufficiency (7%). Steroids were required in 3/27 (11%) pts. Disposition: 19 pts removed for PD, 1 for Gr2 irAE; 7 pts remain active on treatment. Median time on treatment: 6 cycles (range 2-22+). Best response by RECIST 1.1: Partial response (PR) in 5/24 (21%) evaluable pts (1 MSI, 4 MSS); minor regression and ≥50% CA 19-9 decline in 2 additional MSS pts for 11+ and 16+ months. PBMC analyses show changes in expression of activating and inhibitory markers including PD-1 on various immune cell populations. Conclusions: PEM plus induction GM-CSF is safe and tolerable in ABC. Durable radiographic and tumor marker responses including MSS pts warrant further study. PFS6, OS, and correlative analyses are ongoing. Clinical trial information: NCT02703714.

Clinicopathologic characteristics and impact of oophorectomy for ovarian metastases (ovmets) in colorectal cancer (CRC)

779

Background: As overall survival (OS) with metastatic colorectal cancer (mCRC) and imaging modalities improve, detection of ovmets may be increasing. The ovary is often a sanctuary site for mCRC; however, there is a paucity of data to guide decision-making regarding the role for oophorectomy. Methods: This is a single-institution retrospective review of patients (pts) who received care for mCRC (incl. appendiceal primaries) with ovmets from 2009-2017. Pts were identified through a hospital-based cancer registry, provider recall, and pathology and radiology databases. Clinicopathologic and treatment data were abstracted. Cox proportional hazards models were used to evaluate for associations with OS. Results: Of 108 pts, median age was 50 (range 19-106), 62 (57%) were Caucasian, and 69 (64%) had ovmets at initial CRC diagnosis. Primary tumor location was left-sided in 54 (50%), right-sided in 27 (25%), appendiceal in 18 (17%), and unknown in 9 (8%). Median OS from diagnosis of mCRC was 29.6 months (mo) with median follow-up of 21.9 mo (range 0.77-172.47). Younger age, absence of signet-ring or mucinous features, well/moderately differentiated grade, and resection of primary tumor were associated with improved OS (p < 0.05). Of 83 (76%) pts who underwent oophorectomy median OS was 36.7 mo vs. 25 mo in those who underwent non-operative management (HR 0.54, 95% CI 0.31-0.94, p = 0.03). Among 94 pts with extra-ovarian disease, 70 (74%) underwent oophorectomy; however, no significant difference in median OS was detected vs. those who did not (30.9 vs 25.0 mo, p = 0.07). In a multivariate model, oophorectomy was not associated with OS (HR 0.63, 95% CI 0.29-1.36, p = 0.24). Conclusions: While ovmets have been previously reported as associated with a poor prognosis, the median OS for this cohort was comparable to existing OS data for mCRC pts. Although oophorectomy for ovmets from mCRC was associated with improved OS in univariate analysis, this effect was not significant in the presence of extra-ovarian metastases. Ovmets from mCRC remain a difficult challenge in clinical care. Oophorectomy may improve OS in select cases; however, further evaluation of predictors of benefit is needed.

Randomized trial of irinotecan and cetuximab with or without vemurafenib in BRAF-mutant metastatic colorectal cancer (SWOG S1406)

3505

Background: Metastatic colorectal cancer (mCRC) patients (pts) with BRAFV600 mutations have poor outcomes with standard of care chemotherapy and rarely respond to the BRAF inhibitor vemurafenib. In preclinical models, blockade of BRAFV600 by vemurafenib (V) causes feedback upregulation of EGFR, whose signaling activities can be impeded by cetuximab (C) with anti-tumor activity augmented by irinotecan (I). Methods: Pts with BRAFV600 mutated and extended RAS wild-type mCRC were randomized to irinotecan (180 mg/m2 IV every 14 days) and cetuximab (500 mg/m2 IV every 14 days) with or without vemurafenib (960 mg PO twice daily). Eligible pts had ECOG PS ≤1, and had received 1 or 2 prior regimens with no prior anti-EGFR agents. Randomization was stratified for prior irinotecan. Crossover from the control arm (IC) to the experimental arm (VIC) was allowed after documented progression. The primary endpoint was progression-free survival (PFS, investigator assessed), with 90% power to detect a HR of 0.5, with two-sided type 1 error of 5%. Results: 106 pts were enrolled (99 eligible, 49 in the experimental arm) from 12/2014 to 4/2016, with median age 62 years, 59% female, and 39% with prior irinotecan therapy. PFS was improved with the addition of vemurafenib (HR 0.42, 95% confidence interval [CI] 0.26 to 0.66, P < 0.001) with median PFS of 4.4 (95% CI 3.6 – 5.7) mos vs 2.0 (95% CI 1.8 – 2.1) months. Response rate was 16% vs 4% (P = 0.08), with disease control rate of 67% vs 22%. In pts with no prior irinotecan, median PFS was 5.7 (95% CI 3.0-6.1) months in the VIC arm vs 1.9 (95% CI 1.7 – 2.1) months in the IC arm. Grade 3/4 adverse events higher in the VIC arm included neutropenia (28% vs 7%), anemia (13% vs 0%), and nausea (15% vs 0%). There was no increase in skin toxicity or fatigue. 23 pts (46%) in the IC arm crossed over at the time of progression, with median PFS from crossover of 6.0 months (95% CI 3.7 – 7.4). Overall survival (OS) data will be mature for ASCO 2017. Conclusions: These results demonstrate the clinical benefits of the VIC triplet (vemurafenib, cetuximab, and irinotecan) in pts with treatment-refractory BRAFV600 mutated mCRC, and support VIC as a potential new treatment option in this molecular subset. Clinical trial information: NCT02164916.

Randomized trial of irinotecan and cetuximab with or without vemurafenib in BRAF-mutant metastatic colorectal cancer (SWOG 1406)

520

Background: BRAF V600 mutations are associated with rare objective responses to the mutated BRAF inhibitor vemurafenib in patients with mCRC. Blockade of BRAFV600 by vemurafenib causes feedback upregulation of EGFR, whose signaling activities can be impeded by cetuximab. In murine models of BRAFV600 mCRC, the combination of irinotecan, cetuximab, and vemurafenib leads to greater anti-tumor activity, as suggested by a prior Phase 1B study. Methods: Patients (pts) with BRAFV600 mutated and extended RAS wild-type mCRC were randomized to irinotecan (180 mg/m2 IV every 14 days) and cetuximab (500 mg/m2 IV every 14 days) with or without vemurafenib (960 mg PO twice daily). Patients had received 1 or 2 prior regimens, with no prior anti-EGFR agents, although prior irinotecan was allowed. Crossover from the control arm to the experimental arm was allowed after documented progression. The primary endpoint was progression-free survival (PFS, investigator assessed), with 90% power to detect a HR of 0.5, with two-sided type 1 error of 5%. Results: 106 patients were enrolled (54 in the experimental arm) from 12/2014 to 4/2016, with ECOG PS ≤ 1. Median age of 62 years, 59% female, and prior irinotecan therapy in 39%. PFS was improved with the addition of vemurafenib (HR = 0.42, 95% confidence interval [CI] of 0.26 to 0.66, P < 0.001) with median PFS of 4.4 (95% CI: 3.6 – 5.7) months vs 2.0 (95% CI: 1.8 – 2.1). Response rate was 16% vs 4% (P = 0.09), with disease control rate of 67% vs 22% (P < 0.001). Grade 3/4 adverse events higher in the experimental arm included neutropenia (28% vs 7%), anemia (13% vs 0%), and nausea (15% vs 0%). There was no increase in skin toxicity or fatigue. No new safety signal was observed. Approximately 50% of patients in the control aim crossed over at the time of progression. Overall survival and efficacy at cross-over data remain immature. Conclusions: The addition of vemurafenib to the combination of cetuximab and irinotecan resulted in a prolongation of progression-free survival and a higher disease control rate, indicating that simultaneous EGFR and BRAF inhibition is effective in BRAFV600 mutated CRC. Clinical trial information: NCT02164916.

Vitamin D levels among patients with colorectal cancer (CRC) from the San Francisco Bay area

793

Background: A growing body of literature suggests that 25-hydroxyvitamin D [25(OH)D] levels are inversely related to the risk of developing CRC and that deficiency is associated with CRC-specific mortality. Due to the unique racial-ethnic diversity and UV exposure patterns of the San Francisco Bay Area, we aimed to evaluate vitamin D levels among our CRC patients at time of diagnosis and during treatment. Methods: Permanent residents of the SF Bay Area with a new diagnosis of CRC of any stage were recruited between 2011 and 2015 prior to initiation of therapy. Self-reported data on sun exposure, diet, and exercise patterns were collected. Clinical data including disease stage and primary tumor location were abstracted from charts. Serum 25(OH)D levels at time of diagnosis and at 6-month follow-up were batched and measured using the Liaison XL assay (Heartland Assays). Supplement use was not restricted. Kruskal-Wallis and Pearson correlation tests were used for categorical or continuous variables, respectively, to evaluate the associations of patient characteristics with 25(OH)D levels. Results: Among 94 patients with a new diagnosis of CRC, median 25(OH)D level at baseline was 27.0 ng/mL (range 7.2-59.0); 26% had deficient levels (<20 ng/mL), 39% had insufficient levels (<20 and <30 ng/mL), and 35% had sufficient levels (<30 ng/mL). Race, multivitamin use, vitamin D supplementation, and disease stage were associated with baseline serum 25(OH)D levels (p<0.05). The median change in 25(OH)D from baseline to six months was -0.6 ng/mL (range -19.4-51.7) for patients treated with chemotherapy (n=60) and 1.6 ng/mL (range -6.4-33.2) for patients who did not receive chemotherapy (n=19) (p=0.51). Conclusions: Among patients with a new diagnosis of CRC in the San Francisco Bay area, vitamin D insufficiency was seen in more than half of patients, consistent with reports from other geographic areas. Allowing for vitamin D supplementation, serum 25(OH)D levels did not decrease significantly after 6 months of chemotherapy. We are routinely screening CRC patients for 25(OH)D insufficiency at time of diagnosis and during treatment.

A model of early integration of palliative care into oncology care for patients with metastatic colorectal cancer

142

Background: Current NCCN guidelines recommend that “institutions should develop processes for integrating palliative care into cancer care.” However, it is not clear what the best method is for implementing this integrated care. Palliative care needs specific to patients with metastatic colorectal cancer (mCRC) and best practices for integration of outpatient palliative and oncologic care in mCRC are not well understood. Methods: We conducted a pre-post prospective cohort study to evaluate the palliative care needs of mCRC patients and the implementation of an integrated palliative care program. In both the control and implementation phase, we enrolled patients with mCRC within 90 days of diagnosis or establishing care for mCRC at UCSF. Patients were surveyed regarding their symptoms, quality of life, psychosocial concerns, functional status and understanding of prognosis. During the control phase, patients received usual oncologic care. Based on survey results from the control phase, we designed a palliative care program to target the needs identified. In the intervention phase, patients are receiving longitudinal palliative care integrated into their usual cancer care. Results: The 30 patients in the control phase reported anorexia, fatigue and poor quality of life as their most common symptoms. Common psychosocial challenges were transportation, insurance/financial and difficulty with treatment decisions. Patients also had unrealistic expectations of their prognosis. In order to improve these identified issues, we designed and implemented an integrated palliative care program that includes weekly multidisciplinary meetings with oncology and palliative care providers and proactive palliative care visits from the time of diagnosis, which occur within the oncology clinic at a time that coincides with oncology visits. Conclusions: Physical symptoms, psychosocial concerns and poor prognostic awareness are common among patients with mCRC. We have implemented an integrated palliative care program to address these needs. Evaluation of the effectiveness of this intervention is ongoing.

A phase II study of axitinib in advanced neuroendocrine tumors

Neuroendocrine tumors (NETs) are highly vascular neoplasms overexpressing vascular endothelial growth factor (VEGF) as well as VEGF receptors (VEGFR). Axitinib is a potent, selective inhibitor of VEGFR-1, -2 and -3, currently approved for the treatment of advanced renal cell carcinoma. We performed an open-label, two-stage design, phase II trial of axitinib 5mg twice daily in patients with progressive unresectable/metastatic low-to-intermediate grade carcinoid tumors. The primary end points were progression-free survival (PFS) and 12-month PFS rate. The secondary end points included time to treatment failure (TTF), overall survival (OS), overall radiographic response rate (ORR), biochemical response rate and safety. A total of 30 patients were enrolled and assessable for toxicity; 22 patients were assessable for response. After a median follow-up of 29months, we observed a median PFS of 26.7months (95% CI, 11.4-35.1), with a 12-month PFS rate of 74.5% (±10.2). The median OS was 45.3 months (95% CI, 24.4-45.3), and the median TTF was 9.6months (95% CI, 5.5-12). The best radiographic response was partial response (PR) in 1/30 (3%) and stable disease (SD) in 21/30 patients (70%); 8/30 patients (27%) were unevaluable due to early withdrawal due to toxicity. Hypertension was the most common toxicity that developed in 27 patients (90%). Grade 3/4 hypertension was recorded in 19 patients (63%), leading to treatment discontinuation in six patients (20%). Although axitinib appears to have an inhibitory effect on tumor growth in patients with advanced, progressive carcinoid tumors, the high rate of grade 3/4 hypertension may represent a potential impediment to its use in unselected patients.

Differential radiographic appearance of BRAF V600E mutant metastatic colorectal cancer (mCRC) in patients matched by primary tumor location

554

Background: BRAF mutation status and location of CRC primary each correlate with pattern of metastatic spread. We sought to determine whether presence of a BRAF V600E (BRAF) mutation is differentially associated with sites and appearance of metastatic disease in patients matched by primary tumor location. Methods: 40 patients with BRAF mutant mCRC were matched to 80 patients with BRAF wild-type CRC by location of primary tumor (right colon, left colon or rectum), sex, and age ( < 50; 50+). CT scans were reviewed for disease characterization. BRAF mutation status, clinicopathological characteristics, and sites of metastatic disease were associated using proportion tests. Results: Of the 120 matched patients,60% were female. The distribution of primary tumor locations was: 60% right colon, 30% left colon, and 10% rectum. Median age at diagnosis was 57, range 20-88 yrs. Significantly higher frequencies of peritoneal metastases (p = 0.045) and ascites (p = 0.0038) occurred in patients with BRAF mutant tumors. Among patients with right colon primaries, no significant difference in sites of disease by BRAF mutation status was observed. In patients with left colon primaries, BRAF mutations associated with less frequent liver metastases (42% vs. 79%, p = 0.024) and more frequent ascites (58% vs. 12%, p = 0.0038). Disease was not measurable by RECIST version 1.1 criteria in 20% of patients with BRAF mutations, most often with peritoneal metastases and ascites. Conclusions: Presence of a BRAF V600E mutation associated with a greater proportion of peritoneal metastases and ascites, even among patients matched for primary tumor location. Of 20 patients with BRAF mutant mCRC and peritoneal metastases plus ascites, 6 patients (30%) had disease that was not measurable by RECIST version 1.1. Radiographic characterization provides a window on BRAF mutant mCRC biology and also reveals a challenge for response evaluation on clinical trials. [Table: see text]

Phase II trial of temsirolimus (TEM) plus sorafenib (SOR) in hepatocellular carcinoma (HCC)

TPS501

Background: The multikinase inhibitor SOR prolongs survival in patients with HCC not amenable to curative therapies. In HCC preclinical models, the combination of SOR with an inhibitor of the mammalian target of rapamycin (mTOR) pathway is synergistic, though single-agent mTOR inhibition did not improve survival in HCC patients after failure of SOR in a phase III trial. We previously completed a phase I study of the mTOR inhibitor TEM combined with SOR in 25 HCC patients which identified the maximum tolerated dose as TEM 10 mg IV weekly and SOR 200 mg PO BID. This two-center, phase II study was developed to examine the efficacy of the combination and to explore candidate biomarkers. The study was approved and funded by the National Comprehensive Cancer Network (NCCN) Oncology Research Program from general research support, with activation October 2012. Methods: The study is registered on ClinicalTrials.gov (NCT01687673). Design: Single-arm, one stage phase II trial. Primary endpoint: Time to progression (TTP) by RECIST 1.1. Other endpoints: Progression-free survival, response rate, overall survival, proportion with alpha fetoprotein decline ≥ 50%, toxicity, hepatitis B virus reactivation rate, and exploratory biomarkers including mTOR pathway protein expression in tumor, circulating tumor cells, and blood and tumor micro-RNA profiles. Sample size: 25 evaluable patients are required to detect a difference between the null hypothesis of median TTP < 3 months versus alternate hypothesis of median TTP ≥ 6 months (a clinically-meaningful outcome in advanced HCC), with 1-sided significance level of 10% and power 88% under the exact test. Main eligibility criteria: HCC not amenable to curative therapies, histologically-confirmed, ≥ 1 untreated, radiographically-measurable site of disease. No prior systemic therapy. ECOG ≤ 1. Child-Pugh score ≤ 7 with bilirubin ≤ 2 mg/dL. Treatment and procedures: TEM 10 mg IVweekly plus SOR 200 mg PO BID in 28-day cycles, with collection of archival tumor samples and blood samples at baseline, on treatment, and at progression. Accrual:Sixteen of 25 planned evaluable patients have enrolled. An interim analysis for safety after 30% enrollment met pre-specified target to continue. Clinical trial information: NCT01687673.

S1406: Randomized phase II study of irinotecan and cetuximab with or without vemurafenib in BRAF-mutant metastatic colorectal cancer (mCRC)

TPS790

Background: BRAFV600 mutations are associated with inferior survival and objective responses to the mutated BRAF inhibitor vemurafenib in patients with mCRC. Blockade of BRAFV600 by vemurafenib causes feedback upregulation of EGFR, whose signaling activities can be impeded by cetuximab. In murine models of BRAFV600 mCRC, the addition of irinotecan to vemurafenib and cetuximab leads to greater anti-tumor activity. Recent phase I studies with the combination of BRAF and EGFR inhibition resulted in response rates substantially higher than either agent alone, with objective responses in 4 of 8 BRAFV600 mCRC patients treated with vemurafenib, cetuximab, and irinotecan. Methods: The SWOG 1406 trial (NCT 02164916) is a randomized phase II study of irinotecan (180 mg/m2 IV every 14 days) and cetuximab (500 mg/m2 IV every 14 days) with or without vemurafenib (960 mg PO twice daily). Eligible adult patients have histologically confirmed colorectal adenocarcinoma with metastatic disease. Tumors must have a BRAFV600 mutation and be wild-type for KRAS and NRAS. BRAF testing may be conducted using any CLIA-compliant lab. Alternatively, screening can be provided through a central lab. Patients must have received one or two prior systemic regimens for unresectable locally advanced or metastatic disease and must not have received anti-EGFR agents. Prior treatment with irinotecan is allowed. Patients randomized to the control arm may crossover to the experimental arm at progression. Target enrollment is 78 patients. The primary endpoint is PFS. Optional participation in a co-clinical trial will be offered in selected sites whereby patients’ biopsies will be used to establish patient-derived xenografts to study correlations between patient and PDX with respect to treatment responses and mechanisms of treatment resistance. This trial has support from all adult cooperative groups and utilizes the Central IRB to facilitate study initiation. Conclusions: mCRC patients harboring BRAFV600E mutations may benefit from EGFR and BRAF blockade. We encourage screening for the BRAF mutation early in the course of metastatic disease therapy and for second line therapy on this trial. Clinical trial information: NCT 02164916.

Molecular epidemiology of RAS/RAF-mutant colorectal cancer metastases

470

Background: A comprehensive molecular characterization of primary colorectal cancers (CRC) was recently reported. Less is known about mutation patterns in CRC metastases and association with survival. Our sequencing analysis focused on CRC liver metastases with RAS/RAF mutations, representing a patient population with limited therapeutic options. Methods: DNA was extracted from formalin-fixed paraffin-embedded CRC liver metastases. Fifty tumors found by Sequenom MassARRAY to harbor KRAS, NRAS or BRAF mutations underwent next generation sequencing on the Ion AmpliSeq Comprehensive Cancer Panel of 409 genes. Co-investigators were blinded to Sequenom mutations identified at UCSF. Variants called by Strelka and VarScan were extensively filtered to control the False Positive Rate and find mutations occurring with > 5-10% variant allele frequency compared to normals. The dataset was evaluated for significant co-mutations, biclustering, and population probabilities of mutations. Results: Following sequencing, 37,744 variants were called in 409 genes with a median coverage depth of 1053x. After filtering to minimize false positives, 2335 variants in 315 genes remained. ARID1A and PIK3R1 were the most significantly associated co-mutation pair, P < 3.5e-5. Biclustering showed no stratification of patients; genes stratified only by mutation frequency. Further filtering yielded 1,186 variants present at < 1% allele frequency within 1,000 Genomes, of which 131 variants in 24 genes are referenced in the Catalog of Somatic Mutations in Cancer. In addition to anticipated mutations in mismatch repair genes and the RTK/RAS/PI3K, Wnt, TP53, and TGF beta pathways, infrequent mutations were found in Akt1, mTOR, MET and PPP2R1a. After APC, TP53 was the most commonly mutated gene, in 44% of the tumors (95% cl: 31.1% - 57.8%). Survival was similar with mutation of RAS/RAF plus either TP53 or PIK3CA. Conclusions: Next generation sequencing was used to characterize co-variants in RAS/RAF mutated CRC liver metastases. The complexity of our results is consistent with the clinical observation that targeting RAS/RAF mutated metastatic CRC is a formidable challenge. These analyses may nonetheless inform the design of future clinical trials.

Pharmacodynamic and efficacy analysis of the BRAF inhibitor dabrafenib (GSK436) in combination with the MEK inhibitor trametinib (GSK212) in patients with BRAFV600 mutant colorectal cancer (CRC)

3507

Background: TheBRAF V600 mutation occurs in 5-10% of metastatic CRC, predicts poor prognosis, and may predict lack of response to standard therapy. The combination of inhibitors of BRAF (dabrafenib; D) and MEK (trametinib; T) has shown significant efficacy in BRAF-mutant melanoma. The safety, efficacy, and pharmacodynamic effects of this combination were studied in BRAF-mutant CRC patients (pts). Methods: BRAF mutant CRC pts were enrolled to an initial efficacy cohort of 26 pts and a subsequent pharmacodynamic (PD) expansion cohort that included biopsies of 15 pts at screening and at steady state. So far, 36 pts have enrolled, including 10 in the PD cohort. Eligible pts had previously-treated BRAFV600E mutant stage IV CRC. Pts were treated with D (150mg BID) and T (2mg QD). Additional analyses were performed on available archival tissues. Results: Data are available for 36 pts: ECOG performance status 0 (58%) or 1 (42%), 81% had received ≥ 2 prior chemotherapy regimens, 36% had received prior EGFR inhibitor treatment, and 83% had ≥ 1 biologic therapy. Among 34 pts with >1 restaging assessment as of November 2012, 1 (3%) achieved a complete response (confirmed, on study >12m), 3 (9%) achieved a partial response (1 confirmed to date), and 18 (53%) had stable disease (SD). Minor responses were seen in 7/18 pts (39%) with SD. Median PFS was 3.5 mo (95% CI: 1.8-4.9); overall duration on study range: 0.03–15.2 mo 7 pts (24%) remained on study for ≥6 cycles with 9 pts still on study. The most frequent AEs, any grade, included pyrexia (67%), nausea (56%), fatigue (53%), chills (47%), vomiting (39%), headache (31%), peripheral edema (31%), anemia (28%), and decreased appetite (28%). 2 pts (6%) discontinued due to AEs. Decreased pERK staining vs pre-dose samples was seen in all post-dose samples leading to absolute (49% ±29%) and relative (69% ±28%, normalized to total ERK) reduction in pERK. Conclusions: Further investigation is needed, as this combination is tolerable at full monotherapy doses of each drug, with manageable toxicities, and has activity in a subset of BRAF mutant pts. Updated safety, efficacy, and correlative data will be presented. Clinical trial information: NCT01072175.

Incomplete inhibition of phosphorylation of 4E-BP1 as a mechanism of primary resistance to ATP-competitive mTOR inhibitors

The mammalian target of rapamycin (mTOR) regulates cell growth by integrating nutrient and growth factor signaling and is strongly implicated in cancer. But mTOR is not an oncogene, and which tumors will be resistant or sensitive to new ATP-competitive mTOR inhibitors now in clinical trials remains unknown. We screened a panel of over 600 human cancer cell lines to identify markers of resistance and sensitivity to the mTOR inhibitor PP242. RAS and PIK3CA mutations were the most significant genetic markers for resistance and sensitivity to PP242, respectively; colon origin was the most significant marker for resistance based on tissue type. Among colon cancer cell lines, those with KRAS mutations were most resistant to PP242, while those without KRAS mutations most sensitive. Surprisingly, cell lines with co-mutation of PIK3CA and KRAS had intermediate sensitivity. Immunoblot analysis of the signaling targets downstream of mTOR revealed that the degree of cellular growth inhibition induced by PP242 was correlated with inhibition of phosphorylation of the translational repressor 4E-BP1, but not ribosomal protein S6. In a tumor growth inhibition trial of PP242 in patient-derived colon cancer xenografts, resistance to PP242 induced inhibition of 4E-BP1 phosphorylation and xenograft growth was again observed in KRAS mutant tumors without PIK3CA co-mutation, compared to KRAS WT controls. We show that, in the absence of PIK3CA co-mutation, KRAS mutations are associated with resistance to PP242 and that this is specifically linked to changes in the level of phosphorylation of 4E-BP1.

A novel interaction of genotype, gender, and adjuvant treatment in survival after resection of stage III colon cancer: Results of CALGB 89803

3517

Background: The p53 tumor suppressor is frequently mutated in colon cancer, but the influence of such mutations on survival is remains undefined. We investigated whether domain-specific mutations in p53 are predictive of survival in stage III colon cancer. Methods: p53 was evaluated in an intergroup trial (CALGB 89803) of patients with stage III colon cancer who were randomized to receive adjuvant 5-fluorouracil/leucovorin (5FU/LV) or 5FU/LV with irinotecan (IFL) Tissue was collected to allow correlation of molecular markers with outcomes. p53 was genotyped in 607 patient tumors. Results: p53 mutations were identified in 274 tumors, divided ~ equally between zinc binding and non-zinc binding regions of the DNA binding domain. Overall, p53 status was not predictive of benefit from either adjuvant regimen. Unexpectedly, the 5 year overall survival (OS) of women with tumors harboring non-zinc binding mutations treated with 5FU/LV was 97% compared to OS of 72% for women with p53 wild-type (wt) tumors (p =0.004). Adding irinotecan to 5FU/LV negated this survival benefit (5 year OS of 81% vs. 72%). Conversely, 5 year OS of women harboring tumors with zinc binding mutations who received 5FU/LV was 50% compared to 72% for women with p53 wt tumors (p=0.04). Adding irinotecan to 5FU/LV reversed the poor survival of women with tumors harboring zinc binding mutations and improved 5 year OS (50% vs. 73%; p=0.1). No difference in OS was observed for men on either treatment arm or when genotype was considered. Conclusions: CALGB 89803 demonstrated a lack of survival benefit for stage III colon cancer patients when irinotecan was added to 5FU/LV (IFL). We now show that in the setting of a large clinical trial, refined stratification of women, based upon domain- specific mutations of p53 identifies subsets of patients likely to benefit from, or respond poorly to, adjuvant 5FU/LV. The interaction of p53 genotype, gender, and adjuvant therapy regimen has the potential to be paradigm changing in the treatment of colon cancer, and possibly other malignancies. These data, if validated, suggest that evaluation of p53 genotype and gender may guide clinicians to make rational choices of adjuvant therapy.

A novel interaction of genotype, gender, and adjuvant treatment in survival after resection of stage III colon cancer: Results of CALGB 89803

452

Background: The p53 tumor suppressor gene is frequently mutated in colorectal cancer, but reports on the effect of p53 mutations on response to adjuvant chemotherapy and survival are inconclusive. This study investigates whether p53 mutational status (wild-type, zinc or non-zinc binding mutations) impacts survival following adjuvant therapy containing fluorouracil/leucovorin with or without irinotecan (5FU/LV or IFL) in women and men with stage III colon cancer.

Methods: As part of a retrospective analysis of prospectively accrued data, p53 mutational status was determined for 609 patients with stage III colon cancer who were randomized on CALGB 89803, a phase III adjuvant chemotherapy trial. p53 exons 5-8 were analyzed by direct sequencing or sequencing by hybridization. p53 mutations were identified in 276 tumors (45%), of which 134 were in the zinc binding and 142 were in the non-zinc binding regions of the core domain. Cox regression was used to study the impact of p53 mutational status, sex, and adjuvant chemotherapy on disease-free (DFS) and overall survival (OS).

Results: p53 mutational status did not predict differential survival or response to adjuvant therapy among the 609 patients assessed. However, a significant sex by treatment interaction was observed for both DFS (Pinteraction=0.008) and OS (Pinteraction=0.002). Significant differences in DFS by p53 mutational status were observed among women (logrank P = 0.009). No such differences were observed among men (logrank P = 0.33). Similar results were observed for OS. There was marginal evidence of a treatment-related impact on the interaction between sex and p53 mutational status for both DFS and OS (DFS Pinteraction = 0.07; OS Pinteraction = 0.11). There was a trend toward improved OS when women with zinc binding mutations received IFL versus 5FU/LV (P = 0.08) and toward worse DFS when women with non-zinc binding mutations were treated with IFL versus 5FU/LV (P =0.08).

Conclusions: This exploratory subset analysis suggests that p53 mutational status may be used to predict prognosis in a sex- and potentially chemotherapeutic regimen-specific manner.

Effect of PIK3CA and KRAS mutations on sensitivity to ATP-competitive mTOR inhibitors in a primary xenograft model of colorectal carcinoma

483

Background: The mammalian target of rapamycin (mTOR) regulates cell growth by integrating nutrient and growth factor signaling and has been strongly implicated in cancer. Mutations in KRAS and the PI3K pathway are upstream of mTOR and are common in colorectal carcinoma (CRC). Currently approved mTOR inhibitors are derivatives of the natural product rapamycin and have shown little clinical efficacy in CRC. A new and potentially more efficacious class of ATP-competitive mTOR inhibitors has now entered clinical trials.

Methods: Seeking a more representative preclinical model of CRC, we generated primary xenografts in nude mice of surgically resected specimens of human hepatic colorectal cancer metastases. We then treated xenograft tumors with the selective ATP-competitive mTOR inhibitor PP242 and monitored response by inhibition of tumor growth, changes in histopatholgy, and alterations in signaling pathways. Cell line experiments were performed to support observations made in the patient derived xenografts.

Results: We demonstrate that in contrast to rapamycin, the mTOR inhibitor PP242 is highly effective at inhibiting tumor growth in both the primary xenograft model and in colorectal cancer cell lines. The inhibition of tumor growth in the xenografts and cell lines depended upon the strong inhibition of phosphorylation of mTOR substrate eIF4E binding protein 1 (4EBP1) but was not correlated with inhibition of phosphorylation of S6 kinase (S6K). Cells with mutant KRAS were relatively resistant to PP242 induced growth inhibition and this correlated with reduced inhibition of 4EBP1 phosphorylation. However, these effects were partially rescued in cells in which a co-mutation in PIK3CA resulted in AKT activation.

Conclusions: Our studies reveal the first mTOR inhibitor resistant cell line, the genetic basis for its resistance and most importantly, these findings were revealed through the use of a primary xenograft mouse model which recapitulates morphologically the features of the tumors isolated from patients. We believe ATP-competitive inhibitors may be of limited clinical utility in mutant KRAS tumors, except for those that have concomitant activation of AKT.