Background: Cancer treatment is often costly and time intensive. Paid medical leave can help employed patients with cancer more effectively manage side effects and complete recommended cancer treatments without loss of income. Since 2012, several states have introduced mandatory paid medical leave policies. We examined whether mandatory paid medical leave policies were associated with better survival among working age adults with cancer. Methods: Adults ages 18 to 64 years diagnosed with cancer 2007- 2019 were identified from the Surveillance, Epidemiology, and End Results registry program covering 12 states. The primary outcome was overall survival (OS). The exposure of interest was the presence of state mandatory paid medical leave policies. Difference-in-differences (DID) analyses with additive hazards regression models compared changes in OS from pre- to post- mandatory paid sick leave policy implementation in states with vs. without paid sick leave policies. Models adjusted for year-quarter fixed effects, state fixed effects, state Medicaid expansion status, age, race, sex, marital status, metropolitan residence status, county-level income, cancer site, cancer stage, and insurance status. Clustered standard errors by state were achieved via the cluster bootstrap. The plausibility of the common trends assumption was tested using event study analyses and was satisfied for all analyses. Primary analyses focused on data from 2007-2016, where information on month of diagnosis, county, and insurance coverage status were available (note these variables are not available for 2017-2019), though sensitivity analyses with data through 2019 without these additional variables were conducted. Results: A total of 1,491,208 adults with cancer were identified. In adjusted DID analyses, after policy implementation, 1-year OS improved from 85.0% to 86.4% in states with mandatory medical leave policies compared to 85.1% to 85.6% in states without such policies. This translates to a 0.85% improvement in 1-year OS (hazard DID: -0.0007, 95% CI = -0.0016 to -0.0001, P = .027). The largest improvement was found among the uninsured population (hazard DID: -0.0038, 95% CI = -0.0076 to -0.0011, P = .013). In sensitivity analyses with abbreviated data through 2019, results were similar (DID for 1-year OS: 1.3%; hazard DID: -0.0010, 95% CI = -0.0025, 0.0001, P = .070). Conclusions: State mandatory paid medical leave was associated with improved survival for working-age adults with newly diagnosed cancer, particularly for those who are uninsured. Policy changes that better support patients through cancer treatment may pay off with improved cancer outcomes.