Regional variations in breast cancer among california teachers.
BACKGROUND
Observed regional differences in breast cancer incidence could provide valuable clues to the etiology of this disease. The pattern of historically higher breast cancer rates among residents of California's San Francisco Bay and Southern Coastal areas is evident in the disease experience among members of the California Teachers Study. This large cohort study has followed female professional school employees for cancer incidence since 1995 and has collected extensive information on breast cancer risk factors.


METHODS
Between 1996 and 1999, invasive breast cancer was diagnosed in 1562 of the 115,611 cohort members who could be geocoded to a California address in 1995 and who had no previous breast cancer diagnosis. Adjusted hazard rate ratios (HRs) were estimated through multivariate Cox proportional hazards modeling.


RESULTS
Rates were higher for cohort members in the San Francisco Bay area (HR = 1.22; 95% confidence interval = 1.06-1.40) and Southern Coastal area (1.16; 1.04-1.30) compared with those in the rest of California. The distributions of variables representing socioeconomic status, urbanization, and personal risk factors were consistent with higher risks for cohort members residing in the San Francisco Bay and Southern Coastal areas. Adjustment for these factors, however, did not explain regional differences in incidence, resulting in HRs that remained elevated for these 2 areas.


CONCLUSIONS
Regional differences in breast cancer incidence in this large, well-defined cohort are not easily explained by known risk factors.
California Department of Health Services, Environmental Health Investigations Branch, Oakland, California 94612, USA. preynolds@dhs.ca.gov
Peggy
P
Reynolds
Susan
S
Hurley
Debbie E
DE
Goldberg
Hoda
H
Anton-Culver
Leslie
L
Bernstein
Dennis
D
Deapen
Pamela L
PL
Horn-Ross
David
D
Peel
Richard
R
Pinder
Ronald K
RK
Ross
Dee
D
West
William E
WE
Wright
Argyrios
A
Ziogas
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000208:ethnology / Q000401:mortality; D002140:California / Q000453:epidemiology; D015331:Cohort Studies; D005178:Faculty; D005260:Female; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D016016:Proportional Hazards Models; D012307:Risk Factors; D012959:Socioeconomic Factors