Background: Timely initiation of cancer treatment can improve quality of life and survival. As part of a large, statewide effort aimed at improving cancer care quality, we estimated time from diagnosis to initial treatment among patients with newly diagnosed metastatic cancers. Methods: Using an established linkage of Washington state cancer registry records with claims data from commercial insurers, Medicare, and Medicaid, we identified patients diagnosed with metastatic solid tumors diagnosed between 2017 and 2019. Time to first treatment with chemotherapy (CT), radiation therapy (RT) or hormone therapy (HT) was measured as the number of days from first visit at an oncology clinic to the date of first treatment. Patients seen at multiple oncology clinics were assigned to the clinic with the greatest number of physician visits. We used linear regression to evaluate factors associated with timeliness of care (tumor type, age, sex, race/ethnicity, insurance type, resident neighborhood deprivation, comorbidity). Results: 3,237 patients met inclusion criteria with median time to initial treatment of 34 days (CT 35 days; RT 28 days; HT 37 days). Mean time to treatment was 45.2 days (CT 47.6 days; RT 39.4 days; HT 49.0 days). Factors that were significantly associated with time to initiation of treatment are shown in the Table. Conclusions: Black and Medicaid-enrolled patients with metastatic cancers experience significantly longer times to first treatment. Future research will focus on identifying factors underlying the observed differences so that interventions can be designed to reduce these disparities.