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e13628 Background: Precision medicine has changed treatment practices for patients with cancer. Clinical guidelines recommend tumor marker testing for many types of cancer given its benefits. Studies have demonstrated that tumor marker testing increases use of appropriate targeted therapies which is associated with improved survival, particularly among patients with advanced or metastatic cancer. In March 2018, Medicare issued a national coverage determination (NCD) for next-generation sequencing to facilitate tumor marker testing. Methods: We conducted a retrospective study to assess tumor marker testing among Medicare beneficiaries with cancer from 03/01/2016 through 02/28/2020. Data were obtained from the Virtual Data Warehouses of 6 United States (US) healthcare systems in the Cancer Research Network, a well-established distributed data network for cancer research. Together these systems provide care to a diverse population of over 5.5 million people in the US. The index date was the first observed cancer diagnosis date recorded in the tumor registry during the study period. Subgroup analyses included those with lung, breast, colorectal, or prostate cancers, or those with advanced, metastatic or recurrent cancer. This is part of a larger project that aims to advance methods for scalable and rigorous evaluation of outcomes of coverage policies for genetic tests. Results: We report results from one health system (03/01/2016-3/31/2018) including Medicare beneficiaries ≥65 years and ≥ 90 enrollment days after the index date. Among 2,277 Medicare beneficiaries with cancer, mean (SD) age was 74 (6.8) years, 1,065 (46.8%) were women, 199 (9.9%) had a tumor marker test within 90 days of the index date, and 1072 (47.1%) started a cancer drug therapy within 90 days of the index date. Among Medicare beneficiaries with lung (n=352), breast (n=361) colorectal (n=135) and prostate (n=326) cancers, proportions of patients having tumor marker tests ranged from 2.2% to 12.8% within 90 days of the index date. Among 572 Medicare beneficiaries with advanced, metastatic or recurrent cancer, 59 (10.3%) had a tumor marker test within 90 days of the index date. Conclusions: The relatively low tumor marker testing rate among Medicare beneficiaries with cancer in this health system is consistent with the literature. Analyses are underway to examine changes in tumor marker testing among Medicare beneficiaries after the implementation of the 2018 Medicare NCD.

Purpose Regular use of aspirin is associated with improved survival for patients with colorectal cancer (CRC). However, the timing of and the subtype of CRC that would benefit the most from using aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) in relation to survival is unclear. Patients and Methods In all, 2,419 patients age 18 to 74 years with incident invasive CRC who were diagnosed from 1997 to 2008 were identified from population-based cancer registries in the United States, Canada, and Australia. Detailed epidemiologic questionnaires were administered at study enrollment and at 5-year follow-up. Survival outcomes were completed through linkage to national death registries. BRAF- and KRAS-mutation status, microsatellite instability, and CpG island methylator phenotype were also evaluated. Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% CIs for overall survival (OS) and CRC-specific survival. Results After a median of 10.8 years of follow-up since diagnosis, 381 deaths (100 as a result of CRC) were observed. Compared with nonusers, postdiagnostic aspirin-only users had more favorable OS (HR, 0.75; 95% CI, 0.59 to 0.95) and CRC-specific survival (HR, 0.44; 95% CI, 0.25 to 0.71), especially among those who initiated aspirin use (OS: HR, 0.64; 95% CI, 0.47 to 0.86; CRC-specific survival: HR, 0.40; 95% CI, 0.20 to 0.80). The association between any NSAID use after diagnosis and OS differed significantly by KRAS-mutation status ( Pinteraction = .01). Use of any NSAID after diagnosis was associated with improved OS only among participants with KRAS wild-type tumors (HR, 0.60; 95% CI, 0.46 to 0.80) but not among those with KRAS-mutant tumors (HR, 1.24; 95% CI, 0.78 to 1.96). Conclusion Among long-term CRC survivors, regular use of NSAIDs after CRC diagnosis was significantly associated with improved survival in individuals with KRAS wild-type tumors.

566 Background: While overall incidence and mortality of colorectal cancer (CRC) has declined, incidence and mortality are increasing in those < 50 years old (early-onset CRC). Our objective was to better understand early-onset CRC by comparing tumor characteristics and initial treatment type between early-onset and normal/late-onset CRC. Methods: We used health system and national tumor registries to identify patients diagnosed with adenocarcinoma of the colon or rectum from 2010-2014 at 6 US integrated health systems in the Patient Outcomes To Advance Learning (PORTAL) network. Tumor registry data included: age at diagnosis, stage, grade, anatomic site, histology, number of lymph nodes examined, and receipt of initial systemic therapy (chemotherapy or immunotherapy). Demographics and other patient characteristics were obtained from the EHR. We used logistic regression to calculate adjusted odds ratios (ORs) and 95% confidence intervals (CIs) comparing the distribution of tumor characteristics and treatment patterns in early-onset ( < 50 years old) vs. normal/late-onset CRC. Results: There were 1,424 early-onset and 10,810 normal/late onset CRC cases in our analyses. Compared to normal/late onset cases, patients with early-onset CRC were more likely to be Hispanic, obese, never smokers, and to have Charlson comorbidity scores < 3. After adjustment for patient characteristics, compared to normal/late onset CRC, early-onset CRC was associated with more advanced stage disease (OR for stage 4 vs. stage 1 = 2.8, CI: 2.4-3.4), high grade histology (OR for poorly differentiated/undifferentiated vs. well/moderately differentiated = 1.2, CI: 1.1-1.5), signet ring histology (OR for signet ring vs. non-mucinous adenocarcinoma = 1.7, CI: 1.1, 2.6), and rectal (OR for rectum vs. cecum = 2.4, CI: 1.9-2.9) or left colon location (OR for left colon vs. cecum = 2.2, CI: 1.8-2.8). After adjustment for patient and tumor characteristics, early-onset patients were more likely than normal/late onset patients to have > 12 lymph nodes examined (OR = 1.6, CI: 1.4-1.8) and to receive systemic therapy (OR = 2.8, CI: 2.4, 3.4). Conclusions: Early-onset CRC is associated with aggressive tumor characteristics, distal location, and systemic therapy use.

6573 Background: Early initiation of treatment following a cancer diagnosis is associated with better patient outcomes. Therefore, we compared time to treatment initiation in American Indian/Alaska...

6572 Background: Hospice care should be available to all individuals with terminal cancer, regardless of race or ethnicity. Little is known about end-of-life care for American Indian/Alaska Native ...

451 Background: Classifications for molecular subtypes of colorectal cancer based on microsatellite instability (MSI), the CpG island methylator phenotype (CIMP), and somatic mutations in BRAFV600E and KRAS have been proposed to reflect distinct pathways of colorectal tumorigenesis. We assessed the relationship between these subtype classifications and colorectal cancer survival in a population-based study. Methods: Tumor-markers were evaluated in incident colorectal cancer cases diagnosed between 1997-2007 in western Washington State. Cases were classified into pathway-based subtypes according to the following tumor-marker combinations: (1) traditional pathway [microsatellite stable / low MSI (MSS/MSI-L), non-CIMP, BRAF-wildtype, KRAS-wildtype, n = 631]; (2) MSI-high serrated (MSI-high, CIMP-positive, BRAF-mutated, KRAS-wildtype, N=100); (3) MSS/MSI-L serrated (MSS/MSI-L, CIMP-positive, BRAF-mutated, KRAS-wildtype, n = 55); (4) alternate pathway (MSS/MSI-L, non-CIMP, BRAF-wildtype, KRAS-mutated, n = 353); and (5) MSI-high familial (MSI-high, non-CIMP, BRAF-wildtype, KRAS-wildtype, n = 50). Multiple-imputation was used to classify tumor-marker status for cases with missing data on one to three markers. Differences in survival across subtypes were assessed through multivariable-adjusted Cox regression. Results: Relative to cases of the predominant traditional pathway subtype, cases with MSS/MSI-L serrated and alternate pathway tumor subtypes experienced statistically significantly worse disease-specific survival [hazard ratio (HR) = 2.25, 95% confidence interval (CI): 1.50-3.36 and HR = 1.39, 95% CI: 1.12-1.71, respectively]; cases with MSI-high familial tumors had the most favorable disease-specific prognosis (HR = 0.28, 95% CI: 0.12-0.64). With respect to overall survival, associations were similar but slightly attenuated. Conclusions: In this large, population-based study, colorectal cancer subtype classifications based on integrated pathways were associated with marked differences in survival, highlighting the significance of molecular heterogeneity in colorectal cancer.