Disparities in cancer incidence by rurality in California.

Background: Cancer rates in rural areas across the United States have different patterns than in urban areas. This study examines associations between rurality and incidence for the top 5 cancers in California and evaluates whether these associations vary jointly by sex, race, and ethnicity.

Methods: We used 2015-2019 California Cancer Registry data to compare incidence rate ratios (IRRs) and trends for breast, prostate, lung, colorectal, and skin (melanoma) cancers. We leveraged census tract aggregation zones and 7 levels of percentage rural population (0%, >0% to <10%, 10% to <20%, 20% to <30%, 30% to <40%, 40% to <50%, and 50+%).

Results: Zones with higher proportions of rural population were significantly associated with lower incidence of female breast cancer and prostate cancer, though the trends were not statistically significant overall. Zones with higher proportions of rural population were significantly associated with higher incidence of lung cancer and melanoma. There were no statistically significant trends for colorectal cancer overall. Comparing areas with 50% and over rural population with areas with 0% rural population, the IRR for lung cancer in Hispanic females was higher (IRR = 1.43, 95% confidence interval [CI] = 1.17 to 1.74) than in Hispanic males (IRR = 0.90, 95% CI = 0.72 to 1.11). Also, in areas with 50% or more rural population, the IRR for melanoma was higher in Hispanic females (IRR = 1.75, 95% CI = 1.23 to 2.45) than non-Hispanic White females (IRR = 0.87, 95% CI = 0.80 to 0.95).

Conclusions: Our findings show that rurality is associated with cancer incidence and underscore the importance of jointly examining rural disparities with sex, race, and ethnicity by cancer site.