IMPORTANCE: Many short-term limited duration (STLD) insurance plans do not cover essential health benefits, such as cancer screenings, potentially delaying diagnoses. In October 2018, federal regulations loosened restrictions on STLD plans by extending the allowable duration from 3 months to 36 months. States expanded, restricted, or eliminated the sale or terms of STLD plans, both prior to 2018 and afterwards. The association of state-level policies and late-stage cancer diagnosis is largely undocumented. OBJECTIVE: To examine associations of state-level policies regarding STLD plans and late-stage cancer diagnosis before and after the 2018 federal rule. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional study included adults aged 18 to 64 years newly diagnosed with cancer (January 2016 to February 2020) in 47 states and the District of Columbia from the National Cancer Database. Patients were grouped by state-level STLD plan policies: (1) states continuously prohibited STLD plans before and after 2018
(2) states stopped offering STLD plans after 2018
(3) states allowed the sale of STLD plans with additional restrictions to the 2018 federal rules
(4) states with no additional STLD regulation. Difference-in-differences analyses were conducted to evaluate changes in late-stage diagnoses (stages III/IV) pre-2018 (January 2016 to June 2018) and post-2018 (January 2019 to February 2020) for groups 2, 3, and 4 vs group 1 for all cancers combined and for 5 common cancers, adjusting for sociodemographic factors (age group, sex, metropolitan status, zip code-level poverty), diagnosis year, and state random effect. All analyses were performed from May 2023 to January 2025. EXPOSURES: State-level STLD plan policies. MAIN OUTCOMES AND MEASURES: Change in percentages of late-stage cancer diagnosis. RESULTS: Among 1 289 366 adults newly diagnosed with cancer (mean [SD] age, 53 [9.2] years
536 514 [41.6%] female
73 061 [5.7%] Hispanic, 110 564 [8.6%] non-Hispanic Asian and Pacific Islander and other, 172 246 [13.4%] non-Hispanic Black, 921 722 [71.5%] non-Hispanic White), 604 882 (46.9%) were from group 4 states (no additional STLD regulations). Group 4 had a net increase of 0.76 (95% CI, 0.22-1.29) percentage points (P = .01) and group 3 (some STLD regulations) had a net increase of 0.84 (95% CI, 0.26-1.42) percentage points (P = .005) in late-stage diagnoses compared with group 1 (continuously prohibited STLD plans). Similar patterns were observed for female breast and colorectal cancers. CONCLUSIONS AND RELEVANCE: In this cross-sectional study of state-level policies regarding STLD plans and late-stage cancer diagnosis, loosened federal restrictions on STLD plans in 2018 were associated with a net increase in late-stage cancer diagnoses in states without or with inadequate regulatory protections, underscoring the critical role of state policies in regulating STLD plans.