Background: Ibrutinib is an oral, once daily Bruton’s tyrosine kinase inhibitor and is the only targeted treatment that has demonstrated progression-free survival and overall survival in multiple phase 3 trials across age, fitness, and high-risk markers for CLL/SLL. This study examined the trends in genomic testing and compared outcomes of first line (1L) CLL patients treated with ibrutinib or CIT in clinical practice. Methods: The nationwide Flatiron Electronic Health Record-derived de-identified database (03/04/2016-08/31/2021) was used to select patients with CLL/SLL who had ≥2 clinic visits and started 1L therapy with ibrutinib or CIT. Patient baseline characteristics prior to 1L initiation were compared between the two treatment groups. Propensity score-based inverse probability of treatment weighting (IPTW) was used to adjust for baseline differences between treatment groups. Kaplan-Meier (KM) analysis was used to evaluate time to next treatment (TTNT) from 1L initiation. Two subgroup analyses were performed among patients with high-risk cytogenetic markers (deletion 17p, 11q or unmutated IGHV) and those without IGHV testing. Results: Overall, the rate of testing for high-risk markers remain suboptimal, while cytogenetic testing for del17p or del11q improved from 52.3% to 74.3%, coinciding with approval of ibrutinib for del17p in 2014, IGHV testing remains infrequent and low at 37.7%. 1882 patients (61.4%) received 1L ibrutinib monotherapy (mean age 71, median follow-up 26 months), and 1182 (38.6%) received a CIT regimen (mean age 68, median follow-up 33 months). More patients treated with ibrutinib had a known high-risk cytogenetic marker (44% vs. 34%), especially in those with deletion 17p (15% vs. 4%), than those treated with CIT. Ibrutinib-treated patients significantly decreased risk of initiating a subsequent treatment by 51% (Table), the high-risk group by 60%, and those with unknown IGHV status by 49%. Conclusions: Consistent with clinical trial evidence, treatment with ibrutinib among 1L CLL patients resulted in a statistically significantly lower risk of initiating subsequent treatment than those treated with CIT, both overall and in the subgroups of patients with high-risk cytogenetic markers and patients without IGHV testing. Assessment of cytogenetic/molecular risk status for appropriate treatment is vital to optimize clinical outcomes, especially in the novel agent era. Recent IGHV testing in community practice to assess genetic risk in CLL remains suboptimal.