Breast Cancer Research
 
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Breast cancer incidence and mortality trends in an affluent population: Marin County, California, USA, 1990-1999.
Authors: Christina A Clarke, Sally L Glaser, Dee W West, Rochelle R Ereman, Christine A Erdmann, Janice M Barlow and Margaret R Wrensch

Elevated rates of breast cancer in affluent Marin County, California, were first reported in the early 1990s. These rates have since been related to higher regional prevalence of known breast cancer risk factors, including low parity, education, and income. Close surveillance of Marin County breast cancer trends has nevertheless continued, in part because distinctive breast cancer patterns in well-defined populations may inform understanding of breast cancer etiology.
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Breast cancer in Marin County.
Author: Alice S Whittemore

Two articles previously published in Breast Cancer Research illustrate the high rates of breast cancer in Marin County, a wealthy, urban county immediately northwest of the city of San Francisco. I herein comment on these articles, and on the political/psychological/scientific dilemma presented by regions with high cancer rates, such as Marin County. I discuss possible causes of such cancer "clusters," and conclude with some thoughts about the future.
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Evaluating local differences in breast cancer incidence rates: A census-based methodology (United States).
Authors: Angela Witt Prehn and Dee W. West

OBJECTIVES: We used readily accessible, existing data to assess whether or not geographic variation in breast cancer incidence rates in the San Francisco Bay Area was related to the unequal distribution of known breast cancer risk factors.
METHODS: Cancer registry and 1990 census block-group data were used to look at the associations between breast cancer incidence and known risk factors (including parity, urban/rural status, and socioeconomic indicators) in 25 California counties. Average annual age-adjusted invasive breast cancer incidence rates were calculated for the period 1988-1992, and adjusted morbidity ratios were computed.
RESULTS: While breast cancer incidence in Marin County was 9 percent higher than that of the other 24 counties combined (relative risk = 1.09, 95 percent confidence interval = 1.01-1.18), this increase appeared to be due to the unequal distribution of known risk factors. Block-groups that had a high level of any risk factor had higher incidence rates, regardless of geographic location. After multivariate adjustment, breast cancer incidence no longer differed between Marin and the other counties (adjusted morbidity ratio = 1.02).
CONCLUSIONS: The results suggest that the unequal distribution of known risk factors was responsible for Marin County's high breast cancer incidence rate.
Cancer Causes and Control 1998;9:511-517.
Geographic Excess of Estrogen Receptor-Positive Breast Cancer
Authors: Christopher C. Benz, Christina A Clarke, and Dan H. Moore II

Elevated and more rapidly increasing breast cancer incidence rates have been described for Marin County, California (CA), a homogeneous, high socioeconomic status population for which yearly surveillance is facilitated by its status as a county. The present study evaluates the histology and hormonal phenotype of the excess breast cancer cases occurring in white, non-Hispanic women living in Marin County between 1992 and 2000 and compares them with patterns occurring in the rest of the San Francisco Bay Area (SFBA) and other urban parts of CA. Incidence data for invasive breast cancer histological subtypes and estrogen receptor (ER) and progesterone receptor (PR) status were obtained from the 1992-2000 Surveillance, Epidemiology, and End Results program. Expected numbers for Marin County were computed based on age-specific rates for five other SFBA counties. Incidence rates were age-adjusted to the 2000 United States standard. Marin County breast cancer diagnoses during 1992-2000 compared with other SFBA and other urban CA Surveillance, Epidemiology, and End Results county rates for white, non-Hispanic women consisted of a disproportionate increase in ER+/PR+ tumors. The observed absolute excess (versus expected) numbers of Marin County ER+/PR+ lobular and nonlobular (predominantly ductal) cases were similar; however, the relative increase appeared greatest for lobular breast cancer. The progressive increase in breast cancer incidence rates observed in Marin County over the past decade is occurring in women with high prevalence of risk factors predisposing toward excess development of ER+/PR+ breast cancer.
Cancer Epidemiology, Biomarkers & Prevention 2003 Dec;12(12):1523-7.
Increase in Breast Cancer Incidence in Middle-aged Women during the 1990s
Authors: Angela Witt Prehn, PhD; Christina Clarke, PhD; Barbara Topol, MS; Sally Glaser, PhD; and Dee West, PhD

PURPOSE: The San Francisco Bay Area has a history of high breast cancer incidence rates relative to the rest of the United States. For Marin County, where Bay Area rates are highest and, moreover, have continued to increase over time, age- and tumor-specific incidence trends were compared with the rest of the region.
METHODS: The study included all white women diagnosed with invasive breast cancer in 1988 to 1997 in the five-county Bay Area (N = 19807). Annual age-specific incidence rates and estimated annual percent changes (EAPCs) were calculated for women ages less than 45, 45 to 64, and greater than or equal to age 65.
RESULTS: Women aged 45 to 64 from Marin County experienced a marked increase in breast cancer rates between 1991 and 1997 (EAPC = 8%, p = 0.02), regardless of disease stage or tumor histology. For the youngest and oldest women, no rate differences were observed by region or over time.
CONCLUSIONS: This regional difference in trend by age did not appear to be due to screening mammography or environmental exposures. Cohort exposures to breast cancer risk factors, such as oral contraceptive and/or hormone replacement therapy use, may have contributed to these rate increases. Although the reasons remain unclear, the finding may signal a rising risk of breast cancer in this demographic group.
AEP 2002 Oct;12(7):476-81.
Risk factors for breast cancer in a population with high incidence rates (Adolescent Risk Factor Study)
Authors: Margaret Wrensch, Terri Chew, Georgianna Farren, Janice Barlow, Flavia Belli, Christina Clarke, Christine A. Erdmann, Marion Lee, Michelle Moghadassi, Roni Peskin-Mentzer, Charles P. Quesenberry Jr., Virginia Souders-Mason, Linda Spence, Marisa Suzuki and Mary Gould

BACKGROUND: This report examines generally recognized breast cancer risk factors and years of residence in Marin County, California, an area with high breast cancer incidence and mortality rates.
METHODS: Eligible women who were residents of Marin County diagnosed with breast cancer in 1997-99 and women without breast cancer obtained through random digit dialing, frequency-matched by cases' age at diagnosis and ethnicity, participated in either full in-person or abbreviated telephone interviews.
RESULTS: In multivariate analyses, 285 cases were statistically significantly more likely than 286 controls to report being premenopausal, never to have used birth control pills, a lower highest lifetime body mass index, four or more mammograms in 1990-94, beginning drinking after the age of 21, on average drinking two or more drinks per day, the highest quartile of pack-years of cigarette smoking and having been raised in an organized religion. Cases and controls did not significantly differ with regard to having a first-degree relative with breast cancer, a history of benign breast biopsy, previous radiation treatment, age at menarche, parity, use of hormone replacement therapy, age of first living in Marin County, or total years lived in Marin County. Results for several factors differed for women aged under 50 years or 50 years and over.
CONCLUSIONS: Despite similar distributions of several known breast cancer risk factors, case-control differences in alcohol consumption suggest that risk in this high-risk population might be modifiable. Intensive study of this or other areas of similarly high incidence might reveal other important risk factors proximate to diagnosis.
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