Metastatic small bowel adenocarcinoma: role of metastasectomy and systemic chemotherapy

Background

Metastatic small bowel adenocarcinoma (SBA) has a poor prognosis. Due to its rarity, high-quality data are lacking to guide treatment. This retrospective analysis was conducted to help characterize the treatment options for patients with metastatic SBA while providing clinically meaningful prognostic information.

Patients and methods

In total, 437 patients who initially presented with or developed metastatic SBA between September 1977 and September 2019 were identified from the MD Anderson Tumor Registry. Clinical data were collected from review of the medical record. Overall response rates (ORR), time to progression (TTP), and overall survival (OS) were assessed across various treatments and treatment lines.

Results

The median OS from diagnosis of metastatic disease was 15.9 months [95% confidence interval (CI): 14.3-17.9]. Seventy-five patients (17.1%) underwent metastasectomy, which was associated with a median OS of 34.5 versus 17.1 months among patients who received chemotherapy alone (P < 0.001). Fluoropyrimidine plus platinum (n = 164) was the most common first-line chemotherapy, associated with an ORR of 59% and TTP of 8.1 months. Irinotecan with 5-FU (n = 101) was the most common second-line therapy associated with an ORR of 31% and TTP of 4.0 months. Twenty-two patients received immunotherapy; 5 of 6 patients with deficient mismatch repair (dMMR) responded, while 0 of 16 with proficient mismatch repair (pMMR) responded. Taxane-based chemotherapy was given to 34 patients with an ORR of 21% and a median TTP of 2.4 months. Among 11 patients who received anti-epidermal-growth-factor-receptor (EGFR) monotherapy, the best response was stable disease (SD) in 1 patient.

Conclusions

In well-selected patients with SBA, metastasectomy appears to be associated with improved OS. This improvement was seen across metastasectomy sites, including liver, lung and peritoneal. Anti-programmed cell death protein 1 (PD-1) based immunotherapy was active for dMMR SBA but not pMMR SBA. While taxane-based chemotherapy demonstrates therapeutic activity, the activity of anti-EGFR therapy was limited.

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Metastasectomy for well-selected metastatic SBA patients was associated with improved OS.

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Anti-PD1-based immunotherapy was active for dMMR SBA but not pMMR SBA.

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Taxane-based chemotherapy demonstrated clinical activity in refractory SBA.

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Anti-EGFR therapy demonstrated minimal activity in SBA.

JSCO-ESMO-ASCO-JSMO-TOS: international expert consensus recommendations for tumour-agnostic treatments in patients with solid tumours with microsatellite instability or NTRK fusions

A Japan Society of Clinical Oncology (JSCO)-hosted expert meeting was held in Japan on 27 October 2019, which comprised experts from the JSCO, the Japanese Society of Medical Oncology (JSMO), the European Society for Medical Oncology (ESMO), the American Society of Clinical Oncology (ASCO), and the Taiwan Oncology Society (TOS). The purpose of the meeting was to focus on what we have learnt from both microsatellite instability (MSI)/deficient mismatch repair (dMMR) biomarkers in predicting the efficacy of anti-programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) immunotherapy, and the neurotrophic tyrosine receptor kinase (NTRK) gene fusions in predicting the efficacy of inhibitors of the tropomyosin receptor kinase (TRK) proteins across a range of solid tumour types. The recent regulatory approvals of the anti-PD-1 antibody pembrolizumab and the TRK inhibitors larotrectinib and entrectinib, based on specific tumour biomarkers rather than specific tumour type, have heralded a paradigm shift in cancer treatment approaches. The purpose of the meeting was to develop international expert consensus recommendations on the use of such tumour-agnostic treatments in patients with solid tumours. The aim was to generate a reference document for clinical practice, for pharmaceutical companies in the design of clinical trials, for ethics committees in the approval of clinical trial protocols and for regulatory authorities in relation to drug approvals, with a particular emphasis on diagnostic testing and patient selection.

Phase II study of nab-paclitaxel in refractory small bowel adenocarcinoma and CpG island methylator phenotype (CIMP)-high colorectal cancer

Background

Hypermethylation of promoter CpG islands [CpG island methylator phenotype (CIMP)] represents a unique pathway for the development of colorectal cancer (CRC), characterized by lack of chromosomal instability and a low rate of adenomatous polyposis coli (APC) mutations, which have both been correlated with taxane resistance. Similarly, small bowel adenocarcinoma (SBA), a rare tumor, also has a low rate of APC mutations. This phase II study evaluated taxane sensitivity in SBA and CIMP-high CRC.

Patients and methods

The primary objective was Response Evaluation Criteria in Solid Tumors version 1.1 response rate. Eligibility included Eastern Cooperative Oncology Group performance status 0/1, refractory disease, and SBA or CIMP-high metastatic CRC. Nab-paclitaxel was initially administered at a dose of 260 mg/m2 every 3 weeks but was reduced to 220 mg/m2 owing to toxicity.

Results

A total of 21 patients with CIMP-high CRC and 13 with SBA were enrolled from November 2012 to October 2014. The efficacy-assessable population (patients who received at least three doses of the treatment) comprised 15 CIMP-high CRC patients and 10 SBA patients. Common grade 3 or 4 toxicities were fatigue (12%), neutropenia (9%), febrile neutropenia (9%), dehydration (6%), and thrombocytopenia (6%). No responses were seen in the CIMP-high CRC cohort and two partial responses were seen in the SBA cohort. Median progression-free survival was significantly greater in the SBA cohort than in the CIMP-high CRC cohort (3.2 months compared with 2.1 months, P = 0.03). Neither APC mutation status nor CHFR methylation status correlated with efficacy in the CIMP-high CRC cohort. In vivo testing of paclitaxel in an SBA patient-derived xenograft validated the activity of taxanes in this disease type.

Conclusion

Although preclinical studies suggested taxane sensitivity was associated with chromosomal stability and wild-type APC, we found that nab-paclitaxel was inactive in CIMP-high metastatic CRC. Nab-paclitaxel may represent a novel therapeutic option for SBA.

Anti-EGFR-resistant clones decay exponentially after progression: implications for anti-EGFR re-challenge

BACKGROUND

Colorectal cancer (CRC) has been shown to acquire RAS and EGFR ectodomain mutations as mechanisms of resistance to epidermal growth factor receptor (EGFR) inhibition (anti-EGFR). After anti-EGFR withdrawal, RAS and EGFR mutant clones lack a growth advantage relative to other clones and decay; however, the kinetics of decay remain unclear. We sought to determine the kinetics of acquired RAS/EGFR mutations after discontinuation of anti-EGFR therapy.

PATIENTS AND METHODS

We present the post-progression circulating tumor DNA (ctDNA) profiles of 135 patients with RAS/BRAF wild-type metastatic CRC treated with anti-EGFR who acquired RAS and/or EGFR mutations during therapy. Our validation cohort consisted of an external dataset of 73 patients with a ctDNA profile suggestive of prior anti-EGFR exposure and serial sampling. A separate retrospective cohort of 80 patients was used to evaluate overall response rate and progression free survival during re-challenge therapies.

RESULTS

Our analysis showed that RAS and EGFR relative mutant allele frequency decays exponentially (r2=0.93 for RAS; r2=0.94 for EGFR) with a cumulative half-life of 4.4 months. We validated our findings using an external dataset of 73 patients with a ctDNA profile suggestive of prior anti-EGFR exposure and serial sampling, confirming exponential decay with an estimated half-life of 4.3 months. A separate retrospective cohort of 80 patients showed that patients had a higher overall response rate during re-challenge therapies after increasing time intervals, as predicted by our model.

CONCLUSION

These results provide scientific support for anti-EGFR re-challenge and guide the optimal timing of re-challenge initiation.

High prevalence of mutant KRAS in circulating exosome-derived DNA from early-stage pancreatic cancer patients

Background

Exosomes arise from viable cancer cells and may reflect a different biology than circulating cell-free DNA (cfDNA) shed from dying tissues. We compare exosome-derived DNA (exoDNA) to cfDNA in liquid biopsies of patients with pancreatic ductal adenocarcinoma (PDAC).

Patients and methods

Patient samples were obtained between 2003 and 2010, with clinically annotated follow up to 2015. Droplet digital PCR was performed on exoDNA and cfDNA for sensitive detection of KRAS mutants at codons 12/13. A cumulative series of 263 individuals were studied, including a discovery cohort of 142 individuals: 68 PDAC patients of all stages; 20 PDAC patients initially staged with localized disease, with blood drawn after resection for curative intent; and 54 age-matched healthy controls. A validation cohort of 121 individuals (39 cancer patients and 82 healthy controls) was studied to validate KRAS detection rates in early-stage PDAC patients. Primary outcome was circulating KRAS status as detected by droplet digital PCR. Secondary outcomes were disease-free and overall survival.

Results

KRAS mutations in exoDNA, were identified in 7.4%, 66.7%, 80%, and 85% of age-matched controls, localized, locally advanced, and metastatic PDAC patients, respectively. Comparatively, mutant KRAS cfDNA was detected in 14.8%, 45.5%, 30.8%, and 57.9% of these individuals. Higher exoKRAS MAFs were associated with decreased disease-free survival in patients with localized disease. In the validation cohort, mutant KRAS exoDNA was detected in 43.6% of early-stage PDAC patients and 20% of healthy controls.

Conclusions

Exosomes are a distinct source of tumor DNA that may be complementary to other liquid biopsy DNA sources. A higher percentage of patients with localized PDAC exhibited detectable KRAS mutations in exoDNA than previously reported for cfDNA. A substantial minority of healthy samples demonstrated mutant KRAS in circulation, dictating careful consideration and application of liquid biopsy findings, which may limit its utility as a broad cancer-screening method.

Prognostic factors after resection of colorectal liver metastases following preoperative second-line chemotherapy: Impact of RAS mutations

BACKGROUND

After resection of colorectal liver metastases (CLM), RAS mutations are associated with modest survival benefit and second-line chemotherapy confers limited hope for cure.

OBJECTIVE

To evaluate the impact of RAS mutation after second-line chemotherapy for patients undergoing potentially curative liver resection for CLM.

METHODS

Among 1357 patients operated for CLM between January 2005 and November 2014, patients with known RAS mutational status were identified. Outcomes after second-line chemotherapy were analyzed by RAS status.

RESULTS

Among 635 patients undergoing resection of CLM, 46 received second-line chemotherapy before resection, including 14 patients (30%) with RAS mutations. Patients who received second-line chemotherapy had significantly larger and greater number of liver metastases and were more likely to undergo major hepatectomy. Median overall (OS) and recurrence free survival (RFS) were significantly worse among patients requiring second-line chemotherapy (OS: 44.4 vs. 61.1 months, p = 0.021; RFS: 7.3 vs. 12.0 months, p = 0.001). Among patients undergoing liver resection after second-line chemotherapy, RAS mutations were associated with worse median OS and RFS (OS: 35.2 vs. 60.7 months, p = 0.038; RFS: 3.6 vs. 8.3 months, p = 0.015). RAS mutation was the only independent factor associated with OS and RFS. All patients with RAS mutations recurred within 18 months. Among patients with RAS wild-type tumors, the receipt of second-line chemotherapy did not affect OS (p = 0.493).

CONCLUSION

Among patients undergoing resection of CLM after second-line chemotherapy, RAS mutational status is an independent predictor of survival and outweighs other factors to select patients for liver resection.

Utility of a molecular prescreening program in advanced colorectal cancer for enrollment on biomarker-selected clinical trials

BACKGROUND

Incorporation of multiple enrichment biomarkers into prospective clinical trials is an active area of investigation, but the factors that determine clinical trial enrollment following a molecular prescreening program have not been assessed.

PATIENTS AND METHODS

Patients with 5-fluorouracil-refractory metastatic colorectal cancer at the MD Anderson Cancer Center were offered screening in the Assessment of Targeted Therapies Against Colorectal Cancer (ATTACC) program to identify eligibility for companion phase I or II clinical trials with a therapy targeted to an aberration detected in the patient, based on testing by immunohistochemistry, targeted gene sequencing panels, and CpG island methylation phenotype assays.

RESULTS

Between August 2010 and December 2013, 484 patients were enrolled, 458 (95%) had a biomarker result, and 157 (32%) were enrolled on a clinical trial (92 on biomarker-selected and 65 on nonbiomarker selected). Of the 458 patients with a biomarker result, enrollment on biomarker-selected clinical trials was ninefold higher for predefined ATTACC-companion clinical trials as opposed to nonpredefined biomarker-selected clinical trials, 17.9% versus 2%, P < 0.001. Factors that correlated positively with trial enrollment in multivariate analysis were higher performance status, older age, lack of standard of care therapy, established patient at MD Anderson, and the presence of an eligible biomarker for an ATTACC-companion study. Early molecular screening did result in a higher rate of patients with remaining standard of care therapy enrolling on ATTACC-companion clinical trials, 45.1%, in contrast to nonpredefined clinical trials, 22.7%; odds ratio 3.1, P = 0.002.

CONCLUSIONS

Though early molecular prescreening for predefined clinical trials resulted in an increase rate of trial enrollment of nonrefractory patients, the majority of patients enrolled on clinical trials were refractory to standard of care therapy. Within molecular prescreening programs, tailoring screening for preidentified and open clinical trials, temporally linking screening to treatment and optimizing both patient and physician engagement are efforts likely to improve enrollment on biomarker-selected clinical trials.

CLINICAL TRIALS NUMBER

The study NCT number is NCT01196130.

Retreatment with anti-EGFR based therapies in metastatic colorectal cancer: impact of intervening time interval and prior anti-EGFR response

BACKGROUND

This retrospective study aims to investigate the activity of retreatment with anti-EGFR-based therapies in order to explore the concept of clonal evolution by evaluating the impact of prior activity and intervening time interval.

METHODS

Eighty-nine KRAS exon 2-wild-type metastatic colorectal patients were retreated on phase I/II clinical trials containing anti-EGFR therapies after progressing on prior cetuximab or panitumumab. Response on prior anti-EGFR therapy was defined retrospectively per physician-records as response or stable disease ≥6 months. Multivariable statistical methods included a multiple logistic regression model for response, and Cox proportional hazards model for progression-free survival.

RESULTS

Retreatment anti-EGFR agents were cetuximab (n = 76) or cetuximab plus erlotinib (n = 13). The median interval time between prior and retreatment regimens was 4.57 months (range: 0.46-58.7). Patients who responded to the prior cetuximab or panitumumab were more likely to obtain clinical benefit to the retreatment compared to the non-responders in both univariate (p = 0.007) and multivariate analyses (OR: 3.38, 95 % CI: 1.27, 9.31, p = 0.019). The clinical benefit rate on retreatment also showed a marginally significant association with interval time between the two anti-EGFR based therapies (p = 0.053). Median progression-free survival on retreatment was increased in prior responders (4.9 months, 95 % CI: 3.6, 6.2) compared to prior non-responders (2.5 months, 95 % CI, 1.58, 3.42) in univariate (p = 0.064) and multivariate analysis (HR: 0.70, 95 % CI: 0.43-1.15, p = 0.156).

CONCLUSION

Our data lends support to the concept of clonal evolution, though the clinical impact appears less robust than previously reported. Further work to determine which patients benefit from retreatment post progression is needed.

Phase II study of saracatinib (AZD0530) in patients with previously treated metastatic colorectal cancer

BACKGROUND

Src has a critical role in tumor cell migration and invasion. Increased Src activity has been shown to correlate with disease progression and poor prognosis, suggesting Src could serve as a therapeutic target for kinase inhibition. Saracatinib (AZD0530) is a novel selective oral Src kinase inhibitor.

METHODS

Metastatic colorectal cancer patients who had received one prior treatment and had measurable disease were enrolled in this phase 2 study. Saracatinib was administered at 175 mg by mouth daily for 28 day cycles until dose-limiting toxicity or progression as determined by staging every 2 cycles. The primary endpoint was improvement in 4 month progression-free survival. Design of Thall, Simon, and Estey was used to monitor proportion of patients that were progression free at 4 months. The trial was opened with plan to enroll maximum of 35 patients, with futility assessment every 10 patients.

RESULTS

A total of 10 patients were enrolled between January and November 2007. Further enrollment was stopped due to futility. Median progression-free survival was 7.9 weeks, with all 10 patients showing disease progression following radiographic imaging. Median overall survival was 13.5 months. All patients were deceased by time of analysis. Observed adverse events were notable for a higher than expected number of patients with grade 3 hypophosphatemia (n = 5).

CONCLUSION

Saracatinib is a novel oral Src kinase inhibitor that was well tolerated but failed to meet its primary endpoint of improvement in 4 month progression-free survival as a single agent in previously treated metastatic colorectal cancer patients.

Characterizing the patterns of clonal selection in circulating tumor DNA from patients with colorectal cancer refractory to anti-EGFR treatment

INTRODUCTION

KRAS and EGFR ectodomain-acquired mutations in patients with metastatic colorectal cancer (mCRC) have been correlated with acquired resistance to anti-EGFR monoclonal antibodies (mAbs). We investigated the frequency, co-occurrence, and distribution of acquired KRAS and EGFR mutations in patients with mCRC refractory to anti-EGFR mAbs using circulating tumor DNA (ctDNA).

PATIENTS AND METHODS

Sixty-two post-treatment plasma and 20 matching pretreatment archival tissue samples from KRAS (wt) mCRC patients refractory to anti-EGFR mAbs were evaluated by high-sensitivity emulsion polymerase chain reaction for KRAS codon 12, 13, 61, and 146 and EGFR 492 mutations.

RESULTS

Plasma analyses showed newly detectable EGFR and KRAS mutations in 5/62 [8%; 95% confidence interval (CI) 0.02-0.18] and 27/62 (44%; 95% CI 0.3-0.56) samples, respectively. KRAS codon 61 and 146 mutations were predominant (33% and 11%, respectively), and multiple EGFR and/or KRAS mutations were detected in 11/27 (41%) cases. The percentage of mutant allele reads was inversely correlated with time since last treatment with EGFR mAbs (P = 0.038). In the matching archival tissue, these mutations were detectable as low-allele-frequency clones in 35% of patients with plasma mutations after treatment with anti-EGFR mAbs and correlated with shorter progression-free survival (PFS) compared with the cases with no new mutations (3.0 versus 8.0 months, P = 0.0004).

CONCLUSION

Newly detected KRAS and/or EGFR mutations in plasma ctDNA from patients refractory to anti-EGFR treatment appear to derive from rare, pre-existing clones in the primary tumors. These rare clones were associated with shorter PFS in patients receiving anti-EGFR treatment. Multiple simultaneous mutations in KRAS and EGFR in the ctDNA and the decline in allele frequency after discontinuation of anti-EGFR therapy in a subset of patients suggest that several resistance mechanisms can co-exist and that relative clonal burdens may change over time. Monitoring treatment-induced genetic alterations by sequencing ctDNA could identify biomarkers for treatment screening in anti-EGFR-refractory patients.

Improved Survival with Anti-VEGF Therapy in the Treatment of Unresectable Appendiceal Epithelial Neoplasms

BACKGROUND

Currently, cytoreductive surgery and hyperthermic intraperitoneal chemotherapy are accepted treatments for surgically resectable appendiceal epithelial neoplasms. However, for nonsurgical candidates, systemic treatment may be considered. The purpose of this analysis was to determine the benefit of biologic therapy (anti-vascular endothelial growth factor and anti-epidermal growth factor receptor) in addition to systemic chemotherapy in this select patient population.

METHODS

The MD Anderson Cancer Center tumor registry was retrospectively reviewed for systemic treatment-naive appendiceal epithelial neoplasm patients registered between January 2000 to July 2007 for prior cytoreductive surgery and hyperthermic intraperitoneal chemotherapy status, histologic grade, signet ring pathology, systemic chemotherapy, biologic therapy, tumor markers (carcinoembryonic antigen, carbohydrate antigen [CA] 125, and/or CA19-9), progression-free survival (PFS), overall survival (OS), and disease control rate. Kaplan-Meier method, log-rank, and Cox proportional hazard regression models were used for statistical analysis.

RESULTS

A total of 353 patients were identified; 130 patients met the inclusion criteria. Fifty-nine patients received biologic therapy. The use of the anti-vascular endothelial growth factor (VEGF) agent bevacizumab improved both OS (42 months vs. 76 months, hazard ratio 0.49 [95 % confidence interval 0.25-0.94] P = 0.03) and PFS (4 months vs. 9 months, hazard ratio 0.69 [95 % confidence interval 0.47-0.995], P = 0.047) for all histologic subtypes. Moderately differentiated tumors had an improved PFS relative to well-differentiated tumors, 9 months versus 3 months (P = 0.05).

CONCLUSIONS

Bevacizumab in combination with chemotherapy appears to play a role in surgically unresectable appendiceal epithelial neoplasm patients, with an improvement in PFS and OS. Anti-VEGF agents should be strongly considered in the management of patients with higher-grade appendiceal epithelial neoplasms who are suboptimal candidates for surgical resection.

Clinicopathologic characteristics and gene expression analyses of non-KRAS 12/13, RAS-mutated metastatic colorectal cancer

BACKGROUND

KRAS mutations in codons 12 and 13 are present in ∼40% of all colorectal cancers (CRC). Activating mutations in codons 61 and 146 of KRAS and in codons 12, 13, and 61 of NRAS also occur but are less frequent. The clinicopathologic features and gene expression profiles of this latter subpopulation of RAS-mutant colorectal tumors have not yet been clearly defined but in general are treated similarly to those with KRAS 12 or 13 mutations.

PATIENTS AND METHODS

Records of patients with metastatic CRC (mCRC) treated at MD Anderson Cancer Center between December 2000 and August 2012 were reviewed for RAS (KRAS or NRAS) and BRAF mutation status, clinical characteristics, and survival outcomes. To study further with an independent cohort, data from The Cancer Genome Atlas were analyzed to define a gene expression signature for patients whose tumors feature these atypical RAS mutations and explore differences with KRAS 12/13-mutated colorectal tumors.

RESULTS

Among the 484 patients reviewed, KRAS 12/13, KRAS 61/146, NRAS, and BRAF mutations were detected in 47.7%, 3.0%, 4.1%, and 7.4%, respectively, of patients who were tested for each of these aberrations. Lung metastases were more common in both the KRAS 12/13-mutated and atypical RAS-mutated cohorts relative to patients with RAS/BRAF wild-type tumors. Gene expression analyses revealed similar patterns regardless of the site of RAS mutation, and in silico functional algorithms predicted that KRAS and NRAS mutations in codons 12, 13, 61, and 146 alter the protein function and drive tumorgenesis.

CONCLUSIONS

Clinicopathologic characteristics, survival outcomes, functional impact, and gene expression profiling were similar between patients with KRAS 12/13 and those with NRAS or KRAS 61/146-mutated mCRC. These clinical and bioinformatic findings support the notion that colorectal tumors driven by these RAS mutations are phenotypically similar.

Multicenter retrospective analysis of metastatic colorectal cancer (CRC) with high-level microsatellite instability (MSI-H)

BACKGROUND

The microsatellite instability-high (MSI-H) phenotype, present in 15% of early colorectal cancer (CRC), confers good prognosis. MSI-H metastatic CRC is rare and its impact on outcomes is unknown. We describe survival outcomes and the impact of chemotherapy, metastatectomy, and BRAF V600E mutation status in the largest reported cohort of MSI-H metastatic colorectal cancer (CRC).

PATIENTS AND METHODS

A retrospective review of 55 MSI-H metastatic CRC patients from two institutions, Royal Melbourne Hospital (Australia) and The University of Texas MD Anderson Cancer Center (United States), was conducted. Statistical analyses utilized Kaplan-Meier method, Log-rank test, and Cox proportional hazards models.

RESULTS

Median age was 67 years (20-90), 58% had poor differentiation, and 45% had stage IV disease at presentation. Median overall survival (OS) from metastatic disease was 15.4 months. Thirteen patients underwent R0/R1 metastatectomies, with median OS from metastatectomy 33.8 months. Thirty-one patients received first-line systemic chemotherapy for metastatic disease with median OS from the start of chemotherapy 11.5 months. No statistically significant difference in progression-free survival or OS was seen between fluoropyrimidine, oxaliplatin, or irinotecan based chemotherapy. BRAF V600E mutation was present in 14 of 47 patients (30%). BRAF V600E patients demonstrated significantly worse median OS; 10.1 versus 17.3 months, P = 0.03. In multivariate analyses, BRAF V600E mutants had worse OS (HR 4.04; P = 0.005), while patients undergoing metastatectomy (HR 0.11; P = <0.001) and patients who initially presented as stage IV disease had improved OS (HR 0.27; P = 0.003).

CONCLUSIONS

Patients with MSI-H metastatic CRC do not appear to have improved outcomes. BRAF V600E mutation is a poor prognostic factor in MSI-H metastatic CRC.

A retrospective study of ampullary adenocarcinomas: overall survival and responsiveness to fluoropyrimidine-based chemotherapy

BACKGROUND

Whether carcinomas of the ampulla of Vater should be classified with biliary tract tumors and treated in a similar manner remains unknown. We sought to compare the outcomes of similarly staged periampullary adenocarcinomas (AAs) and analyze the chemotherapy responsiveness of AAs.

PATIENTS AND METHODS

A total of 905 patients with resected periampullary adenocarcinomas were identified from a prospective surgical registry from 1988 to 2010. A second cohort of 64 metastatic AA patients from 1992 to 2009 who received either front-line fluoropyrimidine-based or gemcitabine-based chemotherapy was also identified.

RESULTS

Overall survival (OS) for AAs was similar to survival with duodenal adenocarcinomas, but was significantly different from both extrahepatic biliary and pancreatic adenocarcinomas (P < 0.001 for each comparison). In multivariate analysis, AAs had a significantly improved OS in comparison with extrahepatic biliary adenocarcinomas (HR = 1.97, P = 0.006). Fluoropyrimidine-based as opposed to gemcitabine-based chemotherapy for metastatic AAs resulted in a significant improvement in time to progression (P = 0.001) but only a trend toward benefit for OS (P = 0.07) in multivariate analysis.

CONCLUSIONS

Differences in the natural history of ampullary and extrahepatic biliary adenocarcinomas exist. Analyses of metastatic ampullary adenocarcinomas suggest that fluoropyrimidine-based chemotherapy may represent a more appropriate front-line chemotherapy approach.

Systemic chemotherapy and surgical cytoreduction for poorly differentiated and signet ring cell adenocarcinomas of the appendix

BACKGROUND

Poorly differentiated and signet ring cell adenocarcinomas of the appendix represent a subset with aggressive tumor biology and poor outcomes with few studies evaluating the impact of systemic chemotherapy and cytoreductive surgery (CRS).

PATIENTS AND METHODS

A retrospective chart review of patients with either poorly differentiated and signet ring cell appendiceal adenocarcinomas was completed from 1992 to 2010.

RESULTS

One hundred forty-two patients were identified. Seventy-eight patients with metastatic disease received chemotherapy. Radiographic response was 44%, median progression-free survival (PFS) was 6.9 months, and median overall survival (OS) was 1.7 years. In multivariate analysis, response to chemotherapy [hazard ratio (HR) 0.5; P = 0.02] predicted improved PFS, and complete CRS (HR 0.3; P = 0.004) predicted improved OS. Patients who underwent complete CRS (n = 26) had a median relapse-free survival (RFS) of 1.2 years and a median OS of 4.2 years. In multivariate analysis for this subset, complete cytoreduction score of 0 was significantly correlated with improved RFS (HR 0.07; P = 0.01) and OS (HR 0.02; P = 0.01).

CONCLUSIONS

Systemic chemotherapy appears to be a viable treatment option for patients with metastatic poorly differentiated and signet ring cell appendiceal adenocarcinomas. Complete CRS is associated with improved RFS and OS, though part of this benefit likely reflects the selection of good tumor biology.

Use of gene expression analysis of periampullary carcinomas to identify biliary-like and intestinal-like subgroups of ampullary and duodenal carcinomas

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Background: Though adenocarcinomas of the ampulla of Vater are classified as biliary cancers, the epithelium of origin and treatment approach for these rare tumors remains controversial. We compared the gene expression profiles of ampullary carcinomas with that of known periampullary carcinomas.

Methods: We analyzed 32 fresh-frozen resected untreated periampullary carcinomas (8 pancreatic, 2 extrahepatic biliary, 8 non-ampullary duodenal, and 14 ampullary) with verified histology and >70% tumor tissue using the Affymetrix U133 Plus 2.0 genome array. Hierarchical clustering of all samples based upon pancreatic and duodenal differentially expressed genes and unsupervised hierarchical clustering was done. Ampullary and duodenal samples were analyzed for histologic subtype (pancreaticobiliary, intestinal, mixed), MSI by PCR, CDX-2 by IHC and KRAS and PI3K mutations by mass spectroscopy-based sequencing (Sequenom).

Results: We identified 3 subgroups: pancreatic (8 pancreatic, 1 duodenal), biliary-like (4 duodenal, 7 ampullary, 2 biliary) and intestinal-like (3 duodenal, 7 ampullary). The intestinal-like subgroup had a significantly improved RFS (p=0.03) and OS (p =0.04) compared to the biliary-like subgroup, after stratification by grade and stage. Unsupervised clustering of only ampullary and duodenal samples identified very similar good prognostic (4 duodenal, 5 ampullary) and bad prognostic groups (3 duodenal, 9 ampullary) with 3-year RFS 75% vs. 31%, p =0.05 and 3-year OS 100% vs. 27%, p =0.01. These 2 groups showed no statistically significant differences in adenoma (56% vs 25%), poor differentiation (11% vs 42%), T4 (33% vs 25%), N1 (67% vs 100%), MSI-high (22% vs 0%), KRAS mutations (33% vs 17%), or PI3K mutations (0% vs 17%). CDX-2 expression (100% vs 50%, p=.04) and intestinal histologic subtype (100% vs 0%, p <0.01) were more common in the good prognostic group.

Conclusions: Gene expression analysis classifies ampullary carcinomas with duodenal carcinomas and identifies a good prognosis intestinal-like group and a poor prognosis biliary-like group. These findings have therapeutic implications.

[Table: see text]

Association of PTEN loss and local recurrence in stage II-III colon cancer

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Background: Activation of the PI3K/Akt signaling pathway by PIK3CA mutations has been associated with increased risk for local recurrence (LR) in rectal cancer patients (pts). We hypothesized that loss of expression of PTEN, a tumor suppressor gene and negative regulator of the PI3K/Akt pathway, may also be associated with increased rates of LR in colon cancer.

Methods: We studied 156 pts with stage II-III colon cancer resected from 1/1990 to 12/2002, including pathology review, PTEN immunohistochemistry, microsatellite instability (MSI) status, 18q loss of heterozygosity (LOH) status and clinical follow-up. PTEN expression with a CLIA-compliant protocol (DAKO antibody) was determined in a tissue microarray with four cores from each tumor and with non-neoplastic mucosa. PTEN loss was defined as complete absence of expression in malignant epithelium with preserved expression of adjoining non-neoplastic tissue serving as a positive control. LR was defined as anastomotic or pericolic peritoneal disease.

Results: 83 M and 73 F pts with median age of 63 were included, with median follow-up of 7.6 yrs. PTEN loss was identified in 26 (16.7%) pts. There were no significant differences in age, sex, T stage, N stage, tumor differentiation, tumor site, lymphovascular invasion (LVI), mucinous component, MSI status or 18q LOH between the PTEN-lost and PTEN-intact groups. The overall survival, relapse-free survival, and distant metastases rate were similar. However, PTEN loss was associated with higher rates of LR (15.4% vs. 4.6%, p = 0.041), and the time to LR was shorter for pts with PTEN loss in their tumor than in PTEN-intact pts (HR 3.3, p = 0.049 by log-rank). LR was associated with LVI, R-sided tumor, 18qLOH, and PTEN loss in univariate analysis. In a multivariate analysis, PTEN loss was associated with a 10.6 fold increased risk of LR (95% CI: 1.7-64.8, p = 0.011).

Conclusions: PTEN loss is associated with a higher rate of and shorter time to LR after resection of colon cancer. This result is consistent with a prior report on the role of PI3K pathway in LR of rectal cancer and suggests that PTEN alteration is a prognostic indicator and that the PI3K/Akt pathway is a potential therapeutic target for these pts.

No significant financial relationships to disclose.

Comparison of ampullary adenocarcinomas and duodenal adenocarcinomas with regard to clinical outcomes and responsiveness to fluoropyrimidine-based chemotherapy

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Background: Though adenocarcinomas of the ampulla of Vater are classified as biliary cancers, the epithelium of origin and treatment approach for these rare tumors remains controversial. Gene expression profiling of periampullary carcinomas (GI ASCO 2011) suggest that ampullary carcinomas are more akin to duodenal than pancreaticobiliary carcinomas.

Methods: Review of a M. D. Anderson Cancer Center (MDACC) periampullary surgical database from 1/1990 to 3/2010 identified 670 pancreatic, 41 extrahepatic biliary, 63 duodenal, and 131 ampullary adenocarcinomas resected at MDACC. Review of the MDACC tumor registry from 5/1990 to 1/2009 identified 240 stage I-III surgically resected ampullary adenocarcinomas seen at MDACC. 46 patients met the following inclusion criteria: MDACC confirmed pathology, distant metastatic relapse, and ≥1 cycle of either gemcitabine or fluoropyrimidine (5-FU) based first-line chemotherapy with follow-up imaging evaluation.

Results: 5-year OS of patients with ampullary cancer did not differ from duodenal cancer (62% vs. 66%, p=0.19) but was significantly different from biliary (24%, p<0.001), and pancreatic cancer (17%, p<0.001). When ampullary (n=131) and duodenal (n=63) cases were stratified by T stage (T1/T2, T3/T4) or N stage (N0, N1) no statistically significant differences in OS were seen. First-line chemotherapy for metastatic ampullary carcinoma was 5-FU based in 27 patients (single agent 8, platinum 18, other 1) and gemcitabine based in 19 patients (single agent 7, platinum 8, other 4). Similar rates of prior adjuvant/neoadjvuant chemotherapy use (55% vs. 64%) and time to distant metastases (18 vs. 17m) were seen in the 5-FU and gemcitabine groups, respectively. 5-FU based chemotherapy was associated with an improved median TTP (9.1m v 4.8m, p=0.05) and trended to improve RR (44% v 21%, p=0.13) and median OS (16m vs. 12.7m, p=0.14).

Conclusions: OS of resected ampullary carcinomas is similar to duodenal carcinomas but not biliary or pancreatic carcinomas. Preliminary data suggest that metastatic ampullary carcinomas may benefit more from a fluoropyrimidine-based as opposed to gemcitabine-based chemotherapy.

[Table: see text]

Neoadjuvant therapy for adenocarcinomas of the duodenum and ampulla of Vater

279

Background: Adenocarcinomas of the ampulla of Vater and duodenum are both rare periampullary tumors with limited data regarding the use of neoadjuvant therapy. We sought to better define the role of neoadjuvant therapy as compared to adjuvant therapy in patients with high-risk disease.

Methods: Retrospective review of the M. D. Anderson Cancer Center (MDACC) tumor registry from 5/1990 to 1/2009 identified 66 cases of ampullary (26 neoadjuvant, 40 adjuvant) and 41 cases of duodenal adenocarcinoma (18 neoadjuvant, 23 adjuvant). Only patients who received adjuvant or neoadjuvant therapy and underwent surgical resection at MDACC where included. High-risk factors were defined as T3 or T4, poor differentiation, or lymph node involvement. Relapse-free survival (RFS) and overall survival (OS) were calculated from the start of surgical resection.

Results: Median age was 61 yrs (range 30-82) and 39% were female. Neoadjuvant (n=44) and adjuvant therapy (n=63) consisted of 5-FU chemoradiation in 93% and 65%, systemic 5-FU based chemotherapy only in 5% and 24%, and gemcitabine or irinotecan based therapy in 2% and 11%, respectively. Pathological high-risk factors were seen in 77% and 95% of neoadjuvant and adjuvant patients, respectively. Indications for neoadjuvant therapy were high risk disease (70%), poor surgical candidate (16%), and concern for possible metastatic disease (14%). In the neoadjuvant group T and N downstaging were observed in 25% and 32% of patients, respectively; 3 patients (7%) had a pathological complete response. Neoadjuvant as compared to adjuvant therapy had similar 5-year OS (66% vs. 59%, p =0.8) and 5-year RFS (54% vs. 59%, p=0.4). Variables significant (p <0.05) in the multivariate analysis for OS were age >60 yrs, lymph node involvement, and margin positivity; and for RFS were lymph node involvement and margin positivity. Neither tumor type (duodenal vs. ampullary; OS HR: 1.6, p =0.2; RFS HR: 0.9, p=0.8) nor treatment type (neoadjuvant vs. adjuvant; OS HR: 1.2, p =0.6; RFS HR: 1.1, p=0.7) were significant for OS or RFS in the multivariate model.

Conclusions: Neoadjuvant therapy appears to be a viable approach for high-risk duodenal and ampullary adenocarcinomas. Further investigation of this treatment approach is needed.

[Table: see text]

Relative value of serum cytokines and clinical factors in predicting weight loss in advanced pancreatic cancer (PC)

208

Background: The identification of PC patients at high risk for cachexia may allow for early intervention to prevent this outcome. Symptoms such as pain, nausea, and anorexia might predict weight loss. Likewise, inflammatory cytokines are also associated with cachexia. We evaluated the ability of each to predict weight loss in patients beginning treatment for PC.

Methods: We evaluated 44 newly diagnosed advanced or metastatic PC patients for baseline symptomatology via the M. D. Anderson Symptom Inventory (MDASI). This survey assesses symptom severity, such as nausea, vomiting, fatigue, pain, diarrhea, and constipation, on a 1-10 scale. Baseline serum levels of IL-1a, IL-1b, IGF-1, CXCL-12, CXCL-16, CRP, IL-6, IL-8, VEGF, CEA, and CA 19-9 were assessed. Logistic regression analysis was performed to determine the odds ratio (OR) and confidence interval (CI) for the association of different parameters with 10% weight loss at 60 days from treatment initiation. Student t-test was used to compare the mean values across different strata.

Results: A weight loss of >10% was observed in 15 patients (34%). Only the use of mild (but not strong) opioids was associated with weight loss; estimated OR = 6.2 (C.I. 1.2-31.9, p=.03). No association was observed for the MDASI parameters. Baseline levels of cytokines were available for 23 patients. We observed significant differences in the mean values of CXCL-16 (p=.05) and IL-6 (p=.045) in patients with weight loss as compared to those without weight loss. Moreover, serum level of erythropoietin may be negatively associated with weight loss (p=0.06).

Conclusions: Alterations in serum cytokine levels may correlate more strongly with cachexia than clinical symptoms and underscore the importance of cytokine analysis in identifying PC patients at high risk for cachexia.

[Table: see text]

Survival advantage associated with palliative oophorectomy in patients with metastatic colorectal cancer (CRC) to the ovaries (mCRC-O): A single institution retrospective analysis

539

Background: The ovaries are an uncommon site for secondary spread from metastatic CRC. We hypothesize that palliative oophorectomy improves survival among patients with mCRC-O.

Methods: We undertook a single institution IRB-approved (DR-09-623) retrospective evaluation of women with mCRC-O from 2001-2008; 110 pts with ovarian metastases and follow-up information for survival analysis were identified out of 3,776 female pts with CRC (2.9%). Survival data was calculated from the date of diagnosis of ovarian metastases (by pathology or radiology) to date of death.

Results: Median age of patients was 49 years (range 19-82); median duration of follow-up was 49 months. Twenty patients were identified from 1,758 female patients with CRC seen at our institution from 2001-2004 (1.1%) and ninety patients identified from 2,018 female CRC patients from 2005-2008 (4.5%). KRAS mutation was present in the primary tumor in 23 of 43 (54%). Sixteen evaluable patients who received systemic chemotherapy with mCRC-O and other sites of metastatic disease were identified; five (31%) had a mixed radiographic response (progression in the ovarian metastases with disease response in other sites of metastases). Seventy-one (64.5%) patients had metastatic disease at the time of initial presentation; 39 (35.5%) had completely resected stage II or III CRC with mCRC-O occurring at a later date. 86 (78.2%) underwent unilateral or bilateral oophorectomy for treatment of their disease. Patients who had metastatic disease at presentation and underwent oophorectomy had a median survival of 39.4 months versus 18.2 months for those with ovarian metastases left in situ (p < 0.0001); patients who developed ovarian relapse after prior colectomy and subsequently underwent oophorectomy had a median survival of 50 months versus 12 months for those patients who did not (p = 0.001). Patients with mCRC-O and peritoneal metastases had a significantly worse survival (p = 0.003).

Conclusions: This single institution retrospective data analysis suggests that women with colorectal cancer metastatic to the ovaries may derive a survival benefit from palliative oophorectomy.

No significant financial relationships to disclose.

Relative impact of chemotherapy with or without bevacizumab on cytokines and angiogenic factors (CAFs) in metastatic colorectal cancer

401

Background: CAFs were previously shown to be modulated in patients (pts) with metastatic colorectal cancer (mCRC) after bevacizumab-containing chemotherapy. Validation of these prior findings is warranted. In addition, the relative impact of bevacizumab and the cytotoxic chemotherapy components on CAFs has not been previously described.

Methods: Plasma samples from 403 mCRC pts were obtained prior to any chemotherapy (Group A) or after progression on a regimen without or with bevacizumab (Group B and C, respectively) between 2002 and 2008. Samples were matched for number of metastatic disease sites (Groups A, B, C) and for prior chemotherapy duration, and time from last chemotherapy dose to sample collection (Groups B, C). Levels of 48 CAFs were measured by suspension bead multiplex assays (BioRad and EMD). Comparisons of Groups A v C (n=169 pairs) and Groups B v C (n=65 pairs) were by the two-sided, nonparametric Wilcoxon paired test, with p<0.05 significance for confirmation of previous CAF results.

Results: Prior chemotherapy duration (6.5mo, 6.7mo), and time from last chemotherapy dose to sample collection (1.3mo, 1.2 mo) were similar for Groups B and C, respectively. Results were available for 80% of the samples. Compared to Group A, Group B had reductions in multiple CAFs, including IL-8 (-38%, p<0.0001) and PDGF (-62%, p<0.0001). Commensurate with prior results, PlGF, Eotaxin and TRAIL were increased in Group C by 30% (p<0.0001), 23% (p=0.024) and 19% (p=0.008) respectively. Most CAF changes were attributable to chemotherapy alone. However, PlGF (-31%, p<0.0001) and TRAIL (+26%, p=0.037) significantly differed in Groups B v C. In group C compared to A, multiple changes were seen in the EGFR-axis including decreases in EGF (-52%, p=0.032), epiregulin (-25%, p=0.0023), and HB-EGF (-40%, p<0.0001) as well as an increase in sEGFR (+10%, p=0.004).

Conclusions: Most changes in CAFs after treatment with bevacizumab-containing chemotherapy appear to be due to chemotherapy alone and not attributable to anti-VEGF therapy, with several notable exceptions. Chemotherapy-induced changes in the EGFR-axis have not previously been described in mCRC and warrant further investigation.

[Table: see text]

Impact of lymph node evaluation on survival for small bowel adenocaricnoma: Analysis of the Surveillance, Epidemiology and End Results (SEER) database

4596

Background: Small bowel adenocarcinoma is a rare malignancy and is often associated with poor outcome. The impact that the number of positive and negative lymph nodes (LN) have upon survival following curative resection has not been studied. Methods: Patients aged 18–90 with adenocarcinoma of the small intestine diagnosed between 1988 and 2005 were identified from SEER data (ver. 2008). Disease-specific survival (DSS) outcomes were determined through 12/2005. Cox proportional hazards regression analyses were performed after adjusting for age, sex, race, T stage, grade, and primary site. Stage I-II cases were categorized by total LN examined (1–8, 9–12, and >12). Stage III cases were evaluated using cut-point analysis to determine the number of positive LN that predicted outcomes. This result was then compared to the predictive value of the ratio of positive to total LN (LNR) using the chi-square statistic. Results: 1,991 patients were identified in the SEER database. Survival among stage I/II patients (n=1,216) was dependent upon the total number of LN assessed. 5-year DSS for stage II patients was 66%, 82% (HR 0.52 95% CI .33-.84), and 88% (HR 0.38, 95% CI .23-.61) for 1–8, 9–12, >12 LN, respectively. The optimal cutpoint of positive LN for stage III disease (n=775) was <3 compard to ≥3 with 5 year DSS of 58% vs. 37% (HR 1.49, 95% CI 1.15–1.92, P=0.002), respectively. Among stage III patients, the LNR was even more predictive of survival than stratification by the number of positive lymph nodes as demonstrated by an improved chi-square statistic for the multivariate model (78.8 vs 63.1, P=0.0005). Conclusions: As noted in colon cancer, the total number of LN assessed has considerable influence upon survival in stage I, II and III small bowel adenocarcinoma. Stratifying stage III small bowel adenocarcinoma into those with <3 and ≥3 positive lymph nodes significantly improves prognostication for these patients and future staging systems should incorporate the number of positive nodes into nodal staging. The use of LNR may provide additional prognostic information.

No significant financial relationships to disclose.

A phase II study of capecitabine and oxaliplatin (CAPOX) in metastatic adenocarcinoma of the small bowel (SBA) or ampulla of Vater

14025

Background: Metastatic SBA and ampullary adenocarcinoma (AAC) are incurable, aggressive malignancies. Limited data exists regarding the role of systemic chemotherapy in these diseases. Given the marked activity of CAPOX in other cancers of the gastrointestinal tract, we have investigated the activity of this combination in these two tumor types. Methods: Patients (pts) with either metastatic or unresectable SBA and AAC who had adequate organ function, ECOG performance status (PS) ≤2 and measurable disease per modified RECIST criteria were enrolled. Prior use of 5-FU or capecitabine as adjuvant therapy, neoadjuvant therapy, or with radiation was allowed. CAPOX was administered as a 21 day cycle with oxaliplatin 130mg/m2 IV on day 1 and capecitabine 750mg/m2 PO BID days 1–14. Up to 30 pts will be enrolled. The primary endpoint is overall response rate (ORR). Results: Eleven pts have been enrolled from 11/04 to 12/05 (6 with AAC and 5 with SBA). Ten pts have received ≥2 cycles and are evaluable for response. All pts had metastatic disease and none had received prior chemotherapy. Patient (pt) characteristics: median age 59 (49–76); M/F (4/7); 91% PS 0–1. Grade 3/4 toxicities included fatigue (5), neuropathy (1), anorexia (1), thrombocytopenia (1), hypokalemia (1), hyponatremia (1), and musculoskeletal (1). Common grade 1/2 toxicities included neuropathy (8), nausea (8), diarrhea (6), and fatigue (5). Four pts required dose reduction and 1 pt discontinued due to toxicity (grade 3 fatigue). Six pts, 3 AAC and 3 SBA, responded with an ORR of 60% (95% CI 31 to 83%). Five responses have been confirmed and 1 AAC pt obtained a complete response after 5 cycles of treatment. Median time to progression was 6.8m (95% CI 4.4 to 9.3+m). Conclusions: The combination of CAPOX is both well-tolerated and highly active. The ORR of 60% is one of the highest yet reported in the literature for the treatment of adenocarcinoma of the small bowel and ampulla of Vater. Enrollment continues on this trial. (Supported by a research grant from Sanofi-Aventis).

[Table: see text]

Doxorubicin-resistant variants of human prostate cancer cell lines DU 145, PC-3, PPC-1, and TSU-PR1: characterization of biochemical determinants of antineoplastic drug sensitivity

Intrinsic and acquired antineoplastic drug resistance remain a major problem for advanced prostate cancer treatment. In order to characterize mechanisms of anti-neoplastic drug resistance in human prostate cancer cell lines, resistant sublines of four of the commonly studied prostate cancer cell lines (DU 145, PC-3, PPC-1, and TSU-PR1) were selected following exposure to increasing concentrations of doxorubicin (from 10-1000 nM). Sensitivity patterns of the parent and doxorubicin-resistant sublines to various anti-neoplastic drugs, including adriamycin, amsacrine, etoposide, camptothecin, vinblastine, vincristine, fluorodeoxyuridine, and melphalan, were determined using a sulforhodamine B growth inhibition assay. The expression of three well-described antineoplastic drug resistance proteins, P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and lung resistance protein (LRP), was assessed using reverse transcriptase-polymerase chain reaction (RT-PCR) assays specific for each of the mRNA species, and using immunocytochemical staining procedures specific for each of the polypeptides. All four of the doxorubicin-selected prostate cancer cell lines exhibited a multidrug resistance phenotype; administration of verapamil restored doxorubicin sensitivity for each of the drug resistant sublines. Although significant MDR1 expression was not detected in any of the parent cell lines before drug exposure by RT-PCR analysis or by immunocytochemistry, both MDR1 mRNA and P-gp protein were expressed by the TSU-PR1 Adr 1000 subline. In contrast, MRP mRNA and protein were present in each of the prostate cancer cell lines before doxorubicin-selection, and an increase in MRP expression appeared to accompany the acquisition of drug resistance in DU 145, PC-3, and PPC-1 doxorubicin-resistant sublines. LRP was variably expressed by each of the parent and resistant cell lines. These data suggest that drug resistance in human prostate cancer may be multifactorial, with MRP and LRP frequently expressed in prostate cancer cells before antineoplastic drug treatment and P-gp expression occasionally acquired after drug exposure.

Amino-terminal deletions enhance aggregation of beta-amyloid peptides in vitro

beta-Amyloid protein, which assembles into pathological aggregates deposited in Alzheimer's disease brain tissue, exhibits N-terminal heterogeneity both in vitro and in vivo. To investigate the effects of this N-terminal heterogeneity on the assembly characteristics and biophysical properties of beta-amyloid, we synthesized a series of peptides with progressively shortened N termini (initial residues at positions beta 1, beta 4, beta 8, beta 12, and beta 17) and C termini extending to residue beta 40 or beta 42. We report that peptides with N-terminal deletions exhibit enhanced peptide aggregation relative to full-length species, as quantitatively assessed by sedimentation analyses. Overall, sedimentation levels were greater for peptides terminating at residue beta 42 than for those terminating at residue beta 40. To determine if established biophysical features of the full-length protein were maintained in the truncated peptides, structural and bioactive properties of these peptides were examined and compared. Full-length and truncated peptides exhibiting aggregation showed circular dichroism spectra consistent with predominant beta-sheet conformation, fibrillar morphology under transmission electron microscopy, and significant toxicity in cultures of rat hippocampal neurons. These data demonstrate that N-terminal deletions enhance aggregation of beta-amyloid into neurotoxic, beta-sheet fibrils and suggest that such peptides may initiate and/or nucleate the pathological deposition of beta-amyloid.