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Purpose Racial/ethnic disparities in cancer survival in the United States are well documented, but the underlying causes are not well understood. We quantified the contribution of tumor, treatment, hospital, sociodemographic, and neighborhood factors to racial/ethnic survival disparities in California. Materials and Methods California Cancer Registry data were used to estimate population-based cancer-specific survival for patients diagnosed with breast, prostate, colorectal, or lung cancer between 2000 and 2013 for each racial/ethnic group (non-Hispanic black, Hispanic, Asian American and Pacific Islander, and separately each for Chinese, Japanese, and Filipino) compared with non-Hispanic whites. The percentage contribution of factors to overall racial/ethnic survival disparities was estimated from a sequence of multivariable Cox proportional hazards models. Results In baseline models, black patients had the lowest survival for all cancer sites, and Asian American and Pacific Islander patients had the highest, compared with whites. Mediation analyses suggested that stage at diagnosis had the greatest influence on overall racial/ethnic survival disparities accounting for 24% of disparities in breast cancer, 24% in prostate cancer, and 16% to 30% in colorectal cancer. Neighborhood socioeconomic status was an important factor in all cancers, but only for black and Hispanic patients. The influence of marital status on racial/ethnic disparities was stronger in men than in women. Adjustment for all covariables explained approximately half of the overall survival disparities in breast, prostate, and colorectal cancer, but it explained only 15% to 40% of disparities in lung cancer. Conclusion Overall reductions in racial/ethnic survival disparities were driven largely by reductions for black compared with white patients. Stage at diagnosis had the largest effect on racial/ethnic survival disparities, but earlier detection would not entirely eliminate them. The influences of neighborhood socioeconomic status and marital status suggest that social determinants, support mechanisms, and access to health care are important contributing factors.

1525 Background: Guidelines recommend consideration of prophylactic surgery for patients with a germline pathogenic variant in some cancer predisposition genes. We assessed surgery utilization in a prospective, multi-institutional cohort study of MGPT. Methods: 2000 patients had MGPT and completed questionnaires at 3, 6, and 12 months. Patients reported surgical utilization and indication (treatment or prevention). Surgery utilization was assessed according to cancer history and MGPT test results: Positive, pathogenic variant; VUS, variant of uncertain significance; Negative, benign variants. Results: Overall, 12.9% (198/1537) of patients reported surgery after MGPT (median follow-up 13 months). Only 31.3% (62/198) of patients specified that their surgery was preventive. Preventive surgery utilization was significantly higher among patients who tested positive (n=30, 14.9%) compared to those testing negative (n=20, 2.3%, p

1582Background: Cancer screening guidelines recommend that germline carriers with a pathogenic variant (PV) in a CRC susceptibility gene should undergo more frequent colonoscopy screening. We asses...

1581Background: Cancer screening guidelines recommend that germline carriers with a pathogenic variant (PV) in a breast cancer susceptibility gene undergo more intensive breast screening including ...

1525 Background: Genetic testing is a powerful tool for stratifying cancer risk. Multiplex gene panel (MGP) testing allows simultaneous analysis of multiple high- and moderate- penetrance genes. However, the diagnostic yield and clinical utility of panels remain to be further delineated. Methods: A report of a fully accrued trial (N = 2000) of patients undergoing cancer-risk assessment. Patients were enrolled in a multicenter prospective cohort study where diagnostic yield and off-target mutation detection was evaluated of a 25 gene MGP comprised of APC, ATM, BARD1, BMPR1A, BRCA1, BRCA2, BRIP1, CDH1, CDK4, CDKN2A, CHEK2, EPCAM, MLH1, MSH2, MSH6, MUTYH, NBN, PALB2, PMS2, PTEN, RAD51C, RAD51D, SMAD4, STK11, TP53. Patients were enrolled if they met standard testing guidelines or were predicted to have a ≥2.5% mutation probability by validated models. Differential diagnoses (DDx) were generated after expert clinical genetics assessment, formulating up to 8 inherited cancer syndromes ranked by estimated likelihood. Results: 1998/2000 patients had reported MGP test results. Women constituted 81% of the sample, and 40% were Hispanic; 241 tested positive for at least 1 pathogenic mutation (12.1%) and 689 (34.5%) patients carried at least 1 variant of uncertain significance. The most frequently identified mutations were in BRCA1 (17%, n = 41), BRCA2 (15%, n = 36), APC (8%, n = 19), CHEK2 (7%, n = 17), ATM (7%, n = 16). 39 patients (16%) had at least 1 pathogenic mutation in a mismatch repair (MMR) gene ( MLH1, n = 10; MSH2, n = 10; MSH6, n = 8; PMS2, n = 11). 43 individuals (18%) had MUTYH mutations – 41 were monoallelic. Among 19 patients who had mutations in APC – 16 were APC I1307K. Only 65% (n = 159) of PV results were included in the DDx, with 35% (n = 86) of mutations not clinically suspected. Conclusions: In a diverse cohort, multiplex panel use increased genetic testing yield substantially: 35% carried pathogenic mutations in unsuspected genes, suggesting a significant contribution of expanded multiplex testing to clinical cancer risk assessment. The identification of off-target mutations broadens our understanding of cancer risk and genotype-phenotype correlations. Follow-up is ongoing to assess the clinical utility of multiplex gene panel testing. Clinical trial information: NCT02324062.

1523 Background: Mutation carrier prediction models are clinically useful tools for identifying candidates for genetic counseling and testing. Consensus guidelines recommend germline genetic testing for those with a carrier probability (CP) of approximately 5% or higher. However, prediction models may perform less well among racial/ethnic minorities. Our hypothesis is that pathogenic mutations (PM) are identifiable in a clinically meaningful fraction of racially/ethnically diverse patients with a CP of < 5%. Methods: We conducted a multicenter prospective clinical trial of patients undergoing cancer-risk assessment using a 25 gene panel, which include APC, ATM, BARD1, BMPR1A, BRCA1, BRCA2, BRIP1, CDH1, CDK4, CDKN2A, CHEK2, EPCAM, MLH1, MSH2, MSH6, MUTYH, NBN, PALB2, PMS2, PTEN, RAD51C, RAD51D, SMAD4, STK11, TP53. Patients were recruited from August 2014 to November 2016 at three centers. Patients were enrolled if they met standard clinical criteria for genetic testing or were predicted to have a ≥2.5% probability of inherited cancer susceptibility using validated prediction models. We evaluated the CP of patients with a PM in BRCA1, BRCA2, and/or a mismatch repair (MMR) gene using the following models: (1) BRCApro, (2) MMRpro and (3) PREMM1,2,6. Results: Of 2000 patients enrolled in this cohort, 80.6% are female (n = 1612). Regarding race/ethnicity, the cohort is 40.1% Non-Hispanic White (n = 802), 37.4% Hispanic (n = 748), 11.5% Asian (n = 230), 3.9% Black (n = 78), and 7.1% Other (n = 142). Among 241 (12.1%) patients who tested positive for a pathogenic mutation, 76 (31.5%) patients had a BRCA1 or BRCA2 mutation. Of those, 52 (68.4%) patients had a BRCApro CP of < 5%. Thirty-eight (15.8%) patients had a pathogenic mutation in an MMR gene: 19 (50.0%) had an MMRpro CP of < 5%, while 13 (34.2%) had a PREMM1,2,6 CP of < 5%. The racial/ethnic distribution of BRCA1/2 or MMR mutation carriers is similar to that of the whole cohort. Conclusions: In a diverse cohort of patients undergoing 25-gene multiple-gene panel testing, half or more carriers of BRCA1/2 or MMR mutations had a CP of < 5%, the consensus guideline-recommended cutoff for genetic testing. These results support a lower threshold for genetic testing guidelines. Clinical trial information: NCT02324062.

1576 Background: Sequencing more genes increases the chance of finding a pathogenic mutation and/or a variant of uncertain significance (VUS). Little is known about potential harms of multiplex testing for cancer risk, such as unwarranted surgery or adverse psychological effects. Methods: We conducted a prospective trial of sequencing 25 genes : APC, ATM, BARD1, BMPR1A, BRCA1, BRCA2, BRIP1, CDH1, CDK4, CDKN2A, CHEK2, EPCAM, MLH1, MSH2, MSH6, MUTYH, NBN, PALB2, PMS2, PTEN, RAD51C, RAD51D, SMAD4, STK11, TP53. Patients were eligible if they met standard testing guidelines or predictive models estimated ≥2.5% mutation probability. Participants were surveyed 3 months post-test: the Multidimensional Impact of Cancer Risk Assessment (MICRA) scale measured distress, uncertainty and positive experiences. We report on the fully accrued trial (N = 2000). Results: 1998/2000 (99.9%) participants currently have reported results: 12.1% tested positive for a pathogenic mutation (Pos), 34.5% had VUS only and 53.5% tested negative (Neg). Median age was 51, 81% were female, 40% Hispanic, and 72% had a cancer history. Self-reported preventive surgery rates were low (mastectomy 9.3%, hysterectomy 1.5%, oophorectomy 1.6%), with no difference between VUS and Neg patients (p = 0.346). Most patients never or rarely had thoughts of cancer affecting daily activities (Pos 59.5%, VUS 66.9%, Neg 71.0%), never regretted testing (Pos 84.1%, VUS 90.0%, Neg 93.6%), and wanted to know all results, even those that doctors do not fully understand (Pos 81.7%, VUS 78.8%, Neg 77.1%). Pos patients had higher MICRA distress and uncertainty scores than VUS and Neg patients, whose distress and uncertainty scores did not differ significantly (p = 0.165, p = 0.129). Relatives of Pos patients completed genetic testing (30.4%) more often than VUS (5.8%) or Neg patients (5.1%, p < 0.001). Conclusions: After multiplex testing of 2000 diverse patients, few reported preventive surgery at 3 months; VUS patients had no more distress, regret or uncertainty than Neg patients. Pos patients most often advised relatives to test, suggesting that participants understood the implications of test results. Longer-term follow-up of test-related outcomes is underway. Clinical trial information: NCT02324062.

1509Background: Genetic testing is a powerful tool for stratifying cancer risk. Multiplex gene panel (MGP) testing allows simultaneous analysis of multiple high- and moderate- penetrance genes. How...

1503Background: Sequencing more genes increases the chance of finding a pathogenic mutation and/or a variant of uncertain significance (VUS). Little is known about potential harms of multiplex test...

7 Background: Multiple-gene sequencing panels are entering clinical practice. We report on research testing with a custom sequencing panel comprising 43 genes and 32 cancer-associated variants among patients referred for assessment of hereditary breast and ovarian cancer risk. Methods: Patients referred to the Stanford Cancer Genetics Program for clinical BRCA1 and BRCA2 (BRCA1/2) mutation testing from 2002-2012 were invited to donate a blood sample for research on an Institutional Review Board-approved protocol. Blood samples were frozen at -80 degrees, and DNA extracted after

374 Background: Screening of persons with newly diagnosed colorectal cancer (CRC) for Lynch Syndrome (LS) can yield substantial population-level benefits at acceptable costs, presuming sufficient uptake of genetic testing by first-degree relatives (FDRs) of LS probands. We reviewed systematically the published literature addressing the frequency and predictors of uptake of genetic testing by FDRs of LS probands. Methods: A literature search was conducted in four electronic databases (CINAHL, PsycInfo, PUBMED, and SCOPUS) for articles published through May 2011 that reported the uptake of genetic testing by relatives of LS probands. Two investigators independently screened articles to determine whether they met inclusion criteria, and abstracted data inthree broad categories: study population, methodology, and uptake of genetic testing. A narrative, qualitative systematic review was performed. The data were not amenable to meta-analysis. Results: 1,258 potentially relevant articles were identified with 533 studies undergoing full text review. Eight articles met inclusion criteria. 52% or less of FDRs of LS probands underwent genetic testing. For each LS proband, 4.6 or fewer relatives underwent genetic testing. Demographic factors (age

6077 Background: When added to first-line chemotherapy for metastatic colorectal cancer, bevacizumab provides a moderate survival increase, but is associated with significant adverse events and high cost. As only a minority of patients respond to antiangiogenic therapy, a diagnostic that identifies potential responders ex ante could potentially change the benefit to risk profile of bevacizumab and likely improve cost-effectiveness. Since efforts to identify a predictive test have so far been unsuccessful, a novel strategy may be to measure tumor response after bevacizumab treatment initiation using an in vivo biomarker test to guide decisions on whether patients should continue treatment. The objective is to estimate the cost-effectiveness of biomarker-directed use of bevacizumab in first-line treatment of metastatic colorectal cancer compared to standard care. Methods: The analysis takes the perspective of the US healthcare system. A decision model was built to estimate the incremental effect of adding bevacizumab to IFL, FOLFIRI, 5FU/LV and FOLOFOX/XELOX regimens. Survival data, estimated through a meta-analysis of four clinical trials, combined with utilities from the literature were used to calculate quality-adjusted life years (QALYs). Costs were based on Medicare reimbursement and expert opinion. Assumed performance characteristics of the biomarker technology (sensitivity, specificity – provided by our industry partner) were 75% and 95% 10 days after commencement of bevacizumab. Results: The biomarker-directed bevacizumab strategy dominated usual care, providing both an average per patient gain of 0.015 QALYs and a cost-savings of $21,038. The cost-effectiveness of the biomarker technology was most influenced by the cost of the test and colorectal cancer utilities. Variations in biomarker specificity and sensitivity changed the magnitude of cost-savings and benefit gain but did not change the overall result of dominance. Conclusions: Modeling predicts that a validated marker which could identify responders to bevacizumab will save money and improve quality-adjusted life years. The results support additional investment in identifying such a diagnostic.