Background: There has been increasing interest in the integration of PROs as part of routine toxicity (tox) assessment and reporting as this may improve tolerance and survival on systemic therapy. Our study aimed to highlight the differential reporting of tox by CRC pts and their providers during Ctx with a focus on actionable tox. We hypothesize that for such tox, under-reporting by providers will be observed less frequently. Methods: With IRB approval, 40 CRC pts undergoing Ctx for CRC at a National Cancer Institute-designated comprehensive cancer center were prospectively enrolled to this observational study. Pts completed PRO-CTCAE forms at the start of therapy and at the subsequent follow up visit. Severity of tox was ranked on a 5-point scale (“none”, “mild”, “moderate”, “severe”, “very severe”). Provider-assessed tox were collected via questionnaires administered in real time (for grade 3+ tox) and also pt chart review. Actionable tox were defined as those that commonly may limit Ctx or require a dose modification (mouth sores, diarrhea, nausea, vomiting, rash, hand-foot syndrome, and neuropathy). Exact McNemar’s test was used to analyze agreement in reporting between patient and provider for each tox. Results: Of 40 pts enrolled, 75% had colon cancer, 70% were Stage IV, and 63% had an ECOG performance status of 0. The median age at enrollment was 55 years and the cohort included 55% male, 80% white, and 58% married adults. Most (93%) pts were treated with chemotherapy (others were on clinical trials with novel agents). Most common grade 3+ tox reported by providers included nausea (10%) and neuropathy (8%), while the common clinically significant tox reported by pts were neuropathy (20%), fatigue (20%), and anxiety (15%). Reported tox were compared to assess degree of agreement in reporting between pts and providers and significant differences were found (Table). Conclusion: Our study provides real world evidence that physicians consistently under-report and document tox from Ctx compared to pts with CRC. This gap did not narrow for actionable tox either. Incorporating PROs in tox reporting and management may provide additional information to physicians to help tailor Ctx and toxicity management plans for an individual pt. Ongoing analysis to correlate tox data with 2-year survival will provide further information about the clinical utility of PROs in ongoing cancer care.