Nutrition and age at first birth in breast-cancer risk

Urbanization and breast cancer incidence in North Carolina, 1995-1999

PURPOSE

Breast cancer incidence rates are reported to be higher in urban compared with rural areas in the United States. We investigated the relationship between urbanization and breast cancer in North Carolina (1995-1999), and considered hospital characteristics as an explanation.

METHODS

We calculated age-adjusted in situ and invasive female breast cancer incidence rates stratified by race, urbanization (Urban Influence Codes), and the presence of a hospital with a cancer registry and cancer program approval in a county.

RESULTS

For white women, incidence rate ratios (IRRs) comparing the most urban with the most rural counties were 1.60 for in situ and 1.18 for invasive cancer. For non-white women, IRRs were 1.27 and 0.99, respectively. IRRs for incidence in registry hospital counties versus those without were all > 1.00 and differences were greater for in situ cancer than invasive. For most strata, urban excesses were attenuated when further stratified by registry hospital status.

CONCLUSIONS

For most strata, we observed excess incidence in urban counties, but it appeared to be explained through the urban preponderance of registry hospitals. Counties with these hospitals may have higher incidence because of increased detection. Area hospital characteristics should be considered when evaluating geographic patterns of breast cancer incidence.

Regional variations in breast cancer incidence among California women, 1988-1997

BACKGROUND

Internationally, California has some of the highest breast cancer rates; these rates also show substantial regional variations within the state. This study describes geographic breast cancer incidence patterns within California and evaluates the degree to which socioeconomic status (SES) and urbanization explain the regional variability.

METHODS

Invasive breast cancer cases in women > or =20 year of age were identified from the California Cancer Registry, for 1988-1997, then assigned to one of three regions (San Francisco Bay Area, Southern Coastal Area and the rest of California), based on residence at diagnosis. Neighborhood SES and urbanization were derived from U.S. Census data. Rate ratios (RR) and 95% confidence intervals (CI) were computed using Poisson regression. Analyses were conducted for all invasive breast cancer cases (n=176,302) and by selected histologic subtypes: ductal (n=121,619); lobular (n=13,410); mixed ductal and lobular (n=9744).

RESULTS

Compared to block groups with the lowest quartile of SES, rates were highest in block groups with high SES. Rates also were higher in suburban and city areas than in small town/rural areas. Compared to the rest of California, age- and race-adjusted rates for all breast cancer were approximately 20% higher in the San Francisco Bay Area and 10% higher in the Southern Coastal Area. After adjusting for SES and urbanization the rate ratios were reduced to near unity (RR=1.06, 95% CI: 1.03-1.09 for San Francisco Bay Area; RR=1.02, 95% CI: 0.99-1.04 for Southern Coastal Area). Rates ratios for ductal carcinomas mirrored those for all cases. For lobular cases, rate ratios remained elevated after adjustment for age, race/ethnicity, neighborhood SES and urbanization (RR=1.18, 95% CI: 1.11-1.27 for San Francisco Bay Area; RR=1.10, 95% CI: 1.04-1.17 for Southern Coastal Area). For the subset of cases with mixed ductal and lobular histologies, the rate ratio for the San Francisco Bay Area was no longer elevated after adjusting for age, race/ethnicity, SES and urbanization (RR=0.92, 95% CI: 0.84-1.01); the adjusted rate ratio for the Southern Coastal Area, however, remained elevated (RR=1.22, 95% CI: 1.12-1.32).

CONCLUSIONS

Regional differences in neighborhood SES and urbanization appear to largely explain regional rate differences in California for all breast cancers and ductal carcinomas but do not fully explain geographic patterns of breast cancer with a lobular component.

Incidence of female breast cancer in relation to prevalence of risk factors in Denmark

The extent to which changes in prevalence of risk determinants for female breast cancer could explain the temporal variation in incidence was examined using incidence figures from Denmark for the years 1943-1989. Significant increases in incidence were observed for more recent time periods and birth cohorts. Using deviance statistics from Poisson regression measures of variability explained, only a small proportion of the increase in incidence could be accounted for by fertility rates, average age at menarche and exposure to exogenous hormones. Dietary factors, on the other hand, accounted for the greater proportion of the variation observed by time period or birth cohort. In particular, there was a strong positive association of incidence with alcohol consumption and a negative association with carbohydrate intake.

Dietary factors in aetiology and prevention of cancer in man

Chemical carcinogenesis, as presently understood, involves a number of carcinogenic factors which act in series of steps. Some industrial carcinogens may pollute the natural environment and penetrate into food. Many substances which are potent carcinogens in experimental animals exist in nature and are present in the human diet. On the other hand, many substances which are known to inhibit experimental carcinogenesis also exist in human diet. The present review discusses experimental and epidemiological data connected with the human cancer and diet. It also postulates that the dietary prevention of human cancer through "prudent" modification of diet and dietary patterns may be of importance; many of the present data are still confusing and conflicting.