Background: Individuals in the USA without private medical insurance are less likely to have access to medical care or participate in cancer screening programmes than those with private medical insurance. Smaller regional studies in the USA suggest that uninsured and Medicaid-insured individuals are more likely to present with advanced-stage cancer than privately insured patients; however, this finding has not been assessed using contemporary, national-level data. Furthermore, patients with cancer from ethnic minorities are more likely to be uninsured or Medicaid-insured than non-Hispanic white people. Separating the effects on stage of cancer at diagnosis associated with these two types of patient characteristics can be difficult. Methods: Patients with cancer in the USA, diagnosed between 1998 and 2004, were identified using the US National Cancer Database-a hospital-based registry that contains patient information from about 1430 facilities. Odds ratios and 95% CIs for the effect of insurance status (Medicaid, Medicare (65-99 years), Medicare (18-64 years), private, or uninsured) and ethnicity (white, Hispanic, black, or other) on disease stage at diagnosis for 12 cancer sites (breast [female], colorectal, kidney, lung, melanoma, non-Hodgkin lymphoma, ovary, pancreas, prostate, urinary bladder, uterus, and thyroid) were estimated, while controlling for patient characteristics. Findings: 3 742 407 patients were included in the analysis; patient characteristics were similar to those of the corresponding US population not included in the analysis. Uninsured and Medicaid-insured patients were significantly more likely to present with advanced-stage cancer compared with privately insured patients. This finding was most prominent for patients who had cancers that can potentially be detected early by screening or symptom assessment (eg, breast, colorectal, and lung cancer, as well as melanoma). For example, the odds ratios for advanced-stage disease (stage III or IV) at diagnosis for uninsured or Medicaid-insured patients with colorectal cancer were 2·0 (95% CI 1·9-2·1) and 1·6 (95% CI 1·5-1·7), respectively, compared with privately-insured patients. For advanced-stage melanoma, the odds ratios were 2·3 (2·1-2·5) for uninsured patients and 3·3 (3·0-3·6) for Medicaid-insured patients compared with privately insured patients. Black and Hispanic patients were noted to have an increased risk of advanced-stage disease (stage III or IV) at diagnosis, irrespective of insurance status, compared with White patients. Interpretation: In this US-based analysis, uninsured and Medicaid-insured patients, and those from ethnic minorities, had substantially increased risks of presenting with advanced-stage cancers at diagnosis. Although many factors other than insurance status also affect the quality of care received, adequate insurance is a crucial factor for receiving appropriate cancer screening and timely access to medical care.
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