Objectives: Alaska Native (AN) women have exhibited some of the highest incidence rates of cancer overall, and different patterns of site-specific incidence compared to other U.S. populations. This study compares incidence rates between AN and U.S. white women (USW) for cancers of the breast, uterus, ovary and cervix, and examines effects of time period and birth cohort as determinants of incidence trends among AN women.
Study design: Observational, population-based study.
Methods: Cancer incidence data from the Alaska Native Tumor Registry and SEERStat, 1974-2003. Age-adjusted World Standard Population rates were calculated for a current 5-year period and over time (30 years), and compared to other populations using rate ratios with 95% confidence intervals. Log-linear regression models used to assess impact on trend of age, time period and birth cohort.
Results: Compared to U.S. white women, current cancer rates among AN women are not significantly different for cancer of the breast and cervix, and significantly lower for cancers of the ovary and uterus. Trends over time over a 30-year time period also differ for these cancer sites. There were significant increases in breast and uterine cancer, and in contrast, a marked decline in cervical cancer. There was no significant change for cancer of the ovary. Changes appear to be due largely to period, not birth cohort effects.
Conclusions: Increases in breast cancer may be due to a combination of modifiable behaviours; increased BMI and a shift to a non-traditional diet. Increases in uterine cancer could be associated with increased BMI and diabetes. Cervical cancer rates have declined to USW levels. The marked decline is likely due to enhanced screening and control efforts within the Alaska Native Women's cancers among Alaska Natives Tribal Health System (formerly Alaska Area USPHS, Indian Health Service utilizing resources available from the Centers for Disease Control tribal and state Breast and Cervical Cancer Early Detection Programs).