PROJECT SUMMARY (ABSTRACT) Early-onset colorectal cancer (EOCRC; CRC diagnosed at < 50 years of age) is a known and worsening public health problem, with alarming increases in incidence across the US, further complicated by lack of healthcare access and poor outcomes among racial and ethnic minorities. Diagnosis for younger patients must rely on symptomatic presentation or another trigger, as routine screening is not recommended for them. Asymptomatic triggers for CRC testing are family history of CRC, precancerous polyps, genetic predisposing syndrome, inflammatory bowel disease, but these represent a small proportion of cases. A much larger proportion of cases have patient report of “red-flag” symptoms (rectal bleeding, abdominal pain, unintentional weight loss, constipation/diarrhea, or iron-deficiency anemia). However, even in the presence of these symptoms, factors at multiple levels contribute to delayed diagnosis: low physician suspicion of cancer, failure to recognize concerning symptoms, overlap of symptoms with other benign disorders, and patients’ lack of knowledge about the disease. Consequently, younger patients are more likely to be misdiagnosed, experience diagnostic delays, report longer duration of symptoms prior to testing, and be diagnosed at later stages. To facilitate earlier diagnoses of EOCRC, we need to better understand prevalence of CRC test orders and receipt for younger symptomatic patients, and explore the association of time-to-testing with cancer diagnoses, especially among uninsured, underserved, minority patients. We have a unique opportunity to generate important information about CRC test order and testing in light of red-flag symptoms among a large and vulnerable group of younger safety-net patients seen in Dallas County’s Parkland Health system. We will use existing electronic health records data (EHR) for patients aged 40-49 years from the current NIH-funded PROSPR cohort study, and extend it by extracting additional Parkland EHR data for those aged 18-39 years, to develop a curated comprehensive colorectal timeline file for those in the “early onset” age range of 18-49. Using data from these under- and uninsured minority patients, we aim to describe EOCRC symptom burden and healthcare system interactions leading to CRC test order and test receipt (Aim 1), and explore association of time-to-testing with cancer stage among patients with EOCRC (Aim 2). Results from this study will generate epidemiologic evidence about CRC testing among younger under- and uninsured symptomatic patients, with efficiency gained from use of 10 years of data from a current NIH- funded cohort study and resultant algorithms. Results from this work can guide development of recommendations generalizable to a diverse group of people, and generate future research questions to understand appropriate EOCRC screening and follow-up in this vulnerable population.