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e16559 Background: ARVs that develop early during treatment with abiraterone acetate/ prednisone (AA/P) may play a role in treatment resistance. We evaluated metastatic site and whole blood mRNA expression of full-length AR (AR-FL) and ARVs to characterize treatment-emergent ARVs (TE-ARVs) from men with mCRPC pre- and post- 12 weeks of AA/P collected in a prospective clinical trial (NCT#01953640). Methods: RNAseq performed on paired metastatic site biopsy (n = 40) and whole blood (n = 25) passed quality control. Reads were aligned to the GRCh38 reference genome with the spliced-alignment TopHat2 package. AR-FL or ARVs were detected if ≥ 2 splice reads aligned to unique splice junctions for AR-FL, AR-8, AR-45, AR-23, AR-V3, AR-V5V6, AR-V7, AR-V8, AR-V9, AR-V10, AR-V12, AR-V13, and AR-V14, and normalized to splice reads per million (SRPM). Cox proportional hazard regression analysis was performed on AR-FL and AR-Vs with ≥1 SRPM for association with time to treatment change (TTTC). Results: In metastatic site biopsies post-AA/P, the average number of splice reads was 27,376,541 (range 7,753,998 to 62,456,773). The median number of ARVs detected was 2 (range 0-8), with a total of total of 110 ARVs identified (Table). Dynamic shifts in ARV profiles were observed post-AAP, with 41 TE-ARVs identified in 17 unique patients. The most common TE-ARV was AR-8 (n = 8), followed by AR-45 (n = 5), AR-23 (n = 5), and AR-V7 (n = 4). The presence of AR-V7 post-AAP was adversely associated with TTTC (hazard ratio 2.46, p = 0.013). The identification of early TE- ARV was not associated with TTTC. In whole blood samples, post-AA/P detection of AR-FL was low (n = 3) and no ARVs were detected. Conclusions: No specific patterns were observed in ARV profiles obtained in the metastatic biopsies after 12 weeks of treatment with AA/P. Clinical trial information: 01953640. [Table: see text]

e16067 Background: Metastatic clear-cell renal cell carcinoma (RCC) is largely incurable, and its treatment remains challenging. Sunitinib, a tyrosine kinase inhibitor, is one of the current standard-of-care options for treatment-naïve patients with metastatic RCC. Despite the proven efficacy of Sunitinib, prolonged treatment with some tyrosine kinase inhibitors (TKIs) has been associated with significant adverse events (AEs). Therefore, we aimed to calculate the exact efficacy in addition to the prevalence of all AEs of Sunitinib in a pooled analysis from all available randomized controlled trials (RCTs). Methods: A comprehensive electronic database search was conducted for all RCTs comparing the clinical outcomes and adverse events of Sunitinib versus all other available treatments for treatment-naïve advanced/metastatic clear-cell renal cell carcinoma. We then calculated the pooled outcomes and prevalence of the most common reported side effects of Sunitinib. All statistical analyses were performed using R Statistical Software v3.4.0 (R Foundation, Vienna, Austria). Results: We included 8 RCTs, with a total of 4106 patients. The mean age was62, with 66.44% males.The efficacy of Sunitinib was reported as 3 main outcomes: Median progression free survival at 10.73 [7.76, 13.7] months, median overall survival at 23.28 [16.74, 29.81] months and the estimated objective response rate at 25[13, 37] %. Any grade AEs were reported in 72% of patients with the following frequencies: fatigue 44%, diarrhea 38%, nausea 31%, hand-foot syndrome 30%, hypertension 27%, dysgeusia 25%, hypothyroidism25%, constipation 20%, stomatitis 20%, inflammation of the mucosa 18%, dyspepsia 16%, vomiting 14%, rash 12%, asthenia 11%, and epistaxis10%.Grade 3&4 (severe) AEs were reported in 52% of patients with the following frequencies: hypertension 9%, fatigue 8%, hand-foot syndrome 5%, asthenia 5%, diarrhea 4%, and inflammation of the mucosa 2%. Conclusions: Despite Sunitinib being one of the current standard treatments for patients with metastatic/advanced clear-cell RCC, with well-described efficacy, its safety profile is still concerning with a significant prevalence of reported grade 3-4 AEs of 52% of the treated patients in the included RCTs. These findings underscore the importance of the emergence of newer drugs and treatment plans for patients with metastatic RCC, not only to achieve similar or better clinical outcomes but also to decrease the percentage of grade 3-4 AEs.

e15698 Background: Neuroendocrine tumors (NETs) and carcinomas (NECs) are a diverse group of tumors with an equally diverse biology and clinical behavior. Data on tissue-based genomic profiling of NETs exists, however, there is limited data using circulating tumor DNA (ctDNA) technology. We sought out to characterize NETs via ctDNA to identify genomic alterations. Methods: 27 patients with metastatic NET/NEC with 32 total plasma samples were analyzed using Guardant360 ctDNA assay. Breakdown of NET/NEC by location: 14 pancreatic NET (pNET), 11 NEC, 1 small bowel NET, 1 lung NET. The ctDNA test detects single nucleotide variants in 54-73 genes, copy number amplifications, fusions, and indels in selected genes. Results: Of the 27 patients, 19 (70%) had a detectable genomic alteration. The detectable (non-synonymous) alterations are as follows: TP53 (n = 14, 70%), NF1 (n = 8, 40%), EGFR (n = 5, 25%), BRCA2 (n = 4, 20%), KRAS (n = 4, 20%), ARID1A (n = 3, 15%), CDK6 (n = 3, 15%), ALK (n = 3, 15%), MET (n = 2, 10%), PTEN (n = 2, 10%), BRAF (n = 2, 10%), MTOR (n = 2, 10%) AKT1 (n = 1), BRCA1 (n = 1), CCND2 (n = 1), CCNE1 (n = 1), CTNNB1 (n = 1), ESR1 (n = 1), FGFR2 (n = 1), HRAS (n = 1), IDH1 (n = 1), KIT (n = 1), MYC (n = 1), NOTCH1 (n = 1), NRAS (n = 1), PDGFRA (n = 1), RAF1 (n = 1), RB1 (n = 1), SMAD4 (n = 1), STK11 (n = 1), TSC1 (n = 1), ERBB2 (n = 1), PIK3CA (n = 1). Conclusions: This experience highlights the feasibility of ctDNA to help identify genomic alterations in this patient population. Further studies incorporating ctDNA testing in this patient population are warranted.

4110 Background: Neuroendocrine tumors (NET) comprise around 2% of all malignant tumors of the gastrointestinal system. The genomic landscape of NET has not been well studied. The aim of this study was to confirm the feasibility of next generation sequencing (NGS) using ctDNA in NET and characterize common alterations in the genomic profile. Methods: Molecular alterations in 114 plasma samples from 114 patients with NET using clinical-grade NGS of ctDNA (Guardant360Ò) across multiple institutions were evaluated. The test detects single nucleotide variants in 54-73 genes, copy number amplifications, fusions, and indels in selected genes. Results: A total of 114 NET patients were evaluated, of which 64 (56.1%) were female. Mean age was 59.7 years with a range between 23-89 years. ctDNA NGS testing was performed on 114 plasma samples; 1 patient had testing performed twice. Genomic alterations were defined in 94 (n = 94/114, 82.5%) samples with a total of 289 alterations identified after excluding variants of uncertain significance (VUSs) and synonymous mutations. Alterations were identified in at least one sample from 83 patients; TP53 associated genes were most commonly altered (n = 83/289, 28.7%), followed by KRAS (n = 22, 7.6%), PI3CA (n = 15, 5.2%), CCNE1 (n = 15, 5.2%), BRAF (n = 13, 4.5%), MYC (n = 12, 4.1%), ERBB2 (n = 11, 3.8%), APC (n = 10, 3.5%), EGFR (n = 10, 3.5%), MET (n = 10, 3.5%), PTEN (n = 9, 3.1%), RB1 (n = 9, 3.1%), CDK6 (n = 7, 2.4%), AR (n = 5, 1.7%), ARID1A (n = 5, 1.7%), FGFR1 (n = 5, 1.7%), and PDGFRA (n = 5, 1.7%). Other genomic alterations of low frequency, but clinical relevance included: CDK4 (n = 4, 1.3%), NF1 (n = 4, 1.3%), RAF1 (n = 4, 1.3%), GNAS (n = 3, 1.0%), KIT (n = 3, 1.3%), BRCA2 (n = 2, 0.7%), CCND2 (n = 2, 0.7%), CTNNB1 (n = 2, 0.7%), JAK2 (n = 2, 0.7%), NRAS (n = 2, 0.7%), SMAD4 (n = 2, 0.7%), and TERT (n = 2, 0.7%). Alterations in AKT1, ALK, ATM, BRCA1, CCND1, CDKN2A, FGFR2, MTOR, RHOA, SMO and STK11 were all reported once (n = 1, 0.3%). Conclusions: Evaluation of ctDNA is feasible among individuals with NET. Liquid biopsies are not invasive and can provide personalized options for targeted therapies in NET patients.

e15066 Background: Circulating cell-free tumor-DNA (ctDNA) testing (‘liquid biopsy’) is increasingly being employed both in clinical trials as well as clinical practice. We aimed to contrast and compare the differences in the number of somatic mutations observed on ctDNA testing between mismatch repair deficient/microsatellite instability-high (dMMR/MSI-High) versus mismatch repair proficient/microsatellite stable (pMMR/MSS) colorectal cancers (CRC). Methods: We had 20 patients at Mayo Clinic Florida that were dMMR/MSI-High with testing through the commercially available platform (Guardant360) that uses a 73-gene panel. Median numbers of somatic mutations were compared between the 2 subset of CRC. Results: Patients with dMMR/MSI-High CRC had a median of 8 mutations (range: 2-15) versus a median of 4 mutations (range: 1-22) in pMMR/MSS patients, p-value of 0.001. Similarly, the mean number of somatic mutations were 7.47 (S.D. ± 4.15) versus 5.02 mutations (S.D. ± 3.83) in patients with dMMR/MSI-H and pMMR/MSS, tumors respectively. Though it is simplistic, we could still potentially identify patients who may be candidates for immunotherapy by gauging the mutational burden reported (Table). Furthermore, on serial testing, decline in mutational burden as early as few weeks into therapy was predictive of response later on imaging. Conclusions: Analysis of number of somatic mutations on ctDNA testing can be complementary to MMR/MSI-testing, especially in situations when tissue is not available or safe to obtain. This can also be of value in predicting and/or following response to immunotherapy. The utility of this may go beyond CRC in identifying patients who may benefit from immunotherapy. [Table: see text]

3566 Background: According to the American Society of Clinical Oncology and College of American Pathologists (ASCO/CAP) joint review on circulating tumor DNA (ctDNA) issued in March 2018, widespread use of ctDNA assays in most patients with advanced cancer is still an area of ongoing research. However, multiple studies thereafter published and/or presented support its use in patients with metastatic colorectal cancer (CRC). This has led to several institutions adopting it as ‘clinical practice’. The aim of this study is to report on our institution’s adoption of ctDNA testing for every patient at the time of diagnosis and/or time of progression. Methods: We report on results of 322 CRC patients with 607 ctDNA tests at our center from January 2017 to February 2019 using a commercially available platform (Guardant360). Results: Among 322 patients of our cohort, a total of 607 ctDNA tests were done (Table). 127 (39.4%) of these tests were serial analyses. In the CRC patients who had serial testing, at progression, mechanisms of resistance included acquisition of KRAS, NRAS, EGFR mutations; and HER2- and MET-amplifications. The subclonal mutations were noted to disappear when the selective inhibition was stopped. This was seen in patients on targeted therapies/biologics rather than chemotherapy. This was of value in treatment modification, clinical trial selection and/or monitoring of disease progression in these patients. Conclusions: While ctDNA testing may not be ready for primetime in all advanced cancers, it is increasingly being adopted in practice for especially metastatic CRC. Of particular value is the serial ctDNA testing in the RAS/RAF wildtype subset and now BRAF V600E mutant CRC on anti-EGFR based therapies. [Table: see text]

1501 Background: Despite BC risk reduction of 50-65% by preventive endocrine therapy (ET), very few at-risk women choose to take them. A woman’s perceived BC risk correlates with uptake of ET. A PRS comprised of 77 BC genetic susceptibility loci (Single Nucleotide Polymorphisms (SNP) improves the accuracy of risk prediction for BC. We examined the impact of the addition of individualized PRS BC risk prediction to standard risk calculator estimates on intent to take BC prevention medication. Methods: Eligible women had ≥5% 10 yr BC Tyrer-Cuzick risk (IBIS) or 5 year Gail score ≥3%, with no history of BC or hereditary BC syndrome. Standard BC risk estimates (IBIS or Gail) were incorporated into the counselling on BC preventive ET. A self-reported questionnaire at baseline quantified intention to take ET and explored factors associated with this decision. Blood samples were obtained and genotyped for 77 SNPs, individualized PRS were calculated then incorporated into IBIS and Gail predictions for 5 yr, 10 yr, & lifetime BC risk. At a second visit, PRS risk & prevention recommendations were revisited. Post visit questionnaires assessed change in intent to take ET. Multivariable linear regression was performed to assess impact of baseline variables on change in intent to take medication. Results: From 2016 to 2017, 151 women in Canada & USA were enrolled, median age: 56.1 (range 36-76.4), 35.6% were premenopausal, 98.7% were Caucasian. Median 5yr, 10yr, & lifetime IBIS risk estimates were 3.8% (2.0-11.5), 7.9% (5.0-23.1), and 25.3% (5.5 to 92.2). PRS increased BC risk estimates in 84 (55.6%) and reduced BC risk estimates in 67 (44%) women. After PRS risk counselling, intention to take ET significantly changed (p<0.001): 41.9% of those with increased PRS were more inclined, and 46.7% of women with decreased PRS were less inclined to take ET. On multivariable regression, increase in PRS (p<0.0001) and less concern about ET side effects (p<0.0001) were associated with greater intent to take ET. Conclusions: In high risk women, PRS significantly changed BC risk estimates & intent to take preventive ET. Further assessments of the impact of PRS scores on compliance with ET are warranted. Clinical trial information: NCT02517593.

1079 Background: Brain metastases (BM) are a common and fatal complication of breast cancer but survival varies widely based on various prognostic factors (PF). Hence, patient counseling and therapeutic decisions should be individualized. We previously published a prognostic index (Breast GPA) based on cohort A (1985-2007, n = 642), updated it with tumor subtype in cohort B (1993-2010, n = 400) and are now updating it with a larger contemporary cohort (C). Methods: A multi-institutional (19) multi-national (3) retrospective database of 2473 breast cancer patients with BM diagnosed from 1/1/2006-12/31/2017 was created and compared to our prior cohorts. Demographic, clinical, molecular factors, tumor subtype and treatment were correlated with survival. Kaplan-Meier survival estimates were calculated and compared with log-rank tests. Results: The median survival (MS) for cohorts A, B and C improved over time [12, 14 and 16 mo, respectively ( < 0.01)] despite the subtype distribution becoming less favorable: Luminal B (ER/PR/HER2+) decreased from 26% to 21%; HER2 (HER2+/ER/PR-) decreased from 31% to 17%, Luminal A (ER/PR+/HER2-) increased from 20% to 31%; Basal (ER/PR/HER2-) was unchanged at 24%.MS by subtype improved from 21 to 27 mo in Luminal B, 18 to 25 mo in HER2, 10 to 14 mo in Luminal A and 6 to 9 mo in Basal tumors. The number of BM was 1 in 35%, ≤4 in 67% and > 10 in 18%. PF significant for survival were tumor subtype, age, KPS, number of BM and extracranial metastases (ECM) (all < 0.01). Surprisingly, Hispanic women (7%) showed improved survival (p < 0.01). BRCA1 was mutated in 57/533 (11%) and those patients showed a trend (0.16) toward improved survival. Treatment patterns have changed: the use of whole brain radiation therapy decreased from 71% to 67% to 47% in cohorts A, B and C, respectively. Conclusions: Despite the shift to less favorable tumor subtypes, MS has improvedbut varies widely by diagnosis-specific PF. Compared to prior cohorts, number of BM and ECM were identified as new PF. Ethnic, genetic and treatment differences between the eras are apparent. The updated Breast GPA, based on these data, and the correlation between BRCA1 and tumor subtype will be presented.

Background and Objectives: Demographic trends show an increasing older adult population. Therefore, family medicine training programs may need to reevaluate how well their residents perform clinic procedures essential to older adults. Our objective was to compare the rates of the most frequently performed clinic procedures for Medicare patients in a large multiregional health care system (MRHCS) with those in a family medicine residency clinic. Methods: In this retrospective cohort study, Current Procedural Terminology coding data were queried from the billing systems of an MRHCS (the control group) and a family medicine residency clinic (the study group) for a 3-year period. The primary outcome was the procedural rate ratios per 1,000 office visits for the 10 most common clinic procedures in the MRHCS billed to Medicare. Results: The study group consisted of 19,099 office visits by Medicare patients to the residency clinic; the control group consisted of 2,034,188 visits to the MRHCS. Except for large joint injection, procedural rates were significantly different for the other nine procedures (destruction of benign skin lesions, nail care, punch or shave skin biopsy, removal of impacted cerumen, wound debridement of skin, Unna boot application, excision of skin lesion, paring of corn or callus, and insertion of bladder catheter). The rate of skin excision was higher in the residency clinic than in the MRHCS but lower for the other eight procedures. Conclusions: These data suggest that teaching programs may need to adapt to meet the current and future practice needs of this increasing patient population.

Abstract Aberrant crypt foci (ACF) are the earliest visible neoplastic lesions in the colorectum. The natural history of these lesions and their role in the adenoma-carcinoma sequence are unknown. We studied ACF in a subset of patients enrolled in the Adenoma Prevention with Celecoxib (APC) Trial to determine whether the presence of ACF in the rectum correlated with that of adenomas in the entire large intestine. Participants were randomized to placebo (n=17), celecoxib 200 mg bid (n=15), or celecoxib 400 mg bid (n=13). Magnification chromoendoscopy (MCE) was performed to identify and biopsy ACF within the rectum at baseline and after 8-12 months of medication use. A total of 670 ACF were identified in 45 patients, and 70 of these were examined histologically. All of the ACF examined were non-dysplastic. Analysis showed no differences in ACF number between baseline and post-treatment studies (8.3±1.0 vs. 6.3±1.1) and no modulation by treatment (celecoxib vs placebo; p=0.77). Immunohistochemical studies showed that ACF contained cells exhibiting increased proliferation, but lacked other features of neoplasia such as increased Cox-2 expression and microvascular density, nuclear localization of β-catenin, or decreased expression of the tumor suppressors SMAD4, estrogen receptor (ERα) or MGMT. Of the secondary markers assessed at baseline, only SMAD4 expression correlated with post-treatment adenoma recurrence. Taken together, these data showed that non-dysplastic ACF are not accurate surrogate endpoint biomarkers of colorectal adenoma risk or NSAID chemoprevention response.