Robert C. Millikan

The health effects of swimming in ocean water contaminated by storm drain runoff

In a case-control study we assessed whether exposure to high job strain during the first 20 weeks of pregnancy increases the risk of preeclampsia and gestational hypertension. Cases (128 with preeclampsia and 201 with gestational hypertension) and controls (N = 401) were primiparous women who had a paid occupation for at least 1 week during the first 20 weeks of their pregnancy and who delivered between 1984 and 1986 in 10 hospitals of Quebec, Canada. Based on their job title, we assigned women scores of psychological demand and decision latitude derived from the National Population Health Survey and classified these women as exposed to high (high demand, low latitude) versus low (low demand, high latitude) job strain. Women exposed to high job strain were more likely to develop preeclampsia [adjusted odds ratio (aOR) = 2.1; 95% confidence interval (CI) = 1.1-4.1] than women exposed to low job strain. The risk was quite similar for women exposed to a full-time, high strain job (> or =35 hours per week) (aOR = 2.0) than in a part-time, high strain job (aOR = 1.8). High job strain increased the risk of gestational hypertension slightly (aOR = 1.3; 95% CI = 0.8-2.2). These results indicate that women exposed to high job strain are at higher risk of developing preeclampsia and, to a lesser extent, gestational hypertension.

Intrinsic Breast Tumor Subtypes, Race, and Long-Term Survival in the Carolina Breast Cancer Study

Purpose: Previous research identified differences in breast cancer–specific mortality across 4 intrinsic tumor subtypes: luminal A, luminal B, basal-like, and human epidermal growth factor receptor 2 positive/estrogen receptor negative (HER2+/ER−). Experimental Design: We used immunohistochemical markers to subtype 1,149 invasive breast cancer patients (518 African American, 631 white) in the Carolina Breast Cancer Study, a population-based study of women diagnosed with breast cancer. Vital status was determined through 2006 using the National Death Index, with median follow-up of 9 years. Results: Cancer subtypes luminal A, luminal B, basal-like, and HER2+/ER− were distributed as 64%, 11%, 11%, and 5% for whites, and 48%, 8%, 22%, and 7% for African Americans, respectively. Breast cancer mortality was higher for participants with HER2+/ER− and basal-like breast cancer compared with luminal A and B. African Americans had higher breast cancer–specific mortality than whites, but the effect of race was statistically significant only among women with luminal A breast cancer. However, when compared with the luminal A subtype within racial categories, mortality for participants with basal-like breast cancer was higher among whites (HR = 2.0, 95% CI: 1.2–3.4) than African Americans (HR = 1.5, 95% CI: 1.0–2.4), with the strongest effect seen in postmenopausal white women (HR = 3.9, 95% CI: 1.5–10.0). Conclusions: Our results confirm the association of basal-like breast cancer with poor prognosis and suggest that basal-like breast cancer is not an inherently more aggressive disease in African American women compared with whites. Additional analyses are needed in populations with known treatment profiles to understand the role of tumor subtypes and race in breast cancer mortality, and in particular our finding that among women with luminal A breast cancer, African Americans have higher mortality than whites. Clin Cancer Res; 16(24); 6100–10. ©2010 AACR.

Mitochondrial DNA G10398A Polymorphism and Invasive Breast Cancer in African-American Women

Mitochondria generate oxygen-derived free radicals that damage mitochondrial DNA (mtDNA) as well as nuclear DNA and in turn promote carcinogenesis. The mtDNA G10398A polymorphism alters the structure of Complex I in the mitochondrial electron transport chain, an important site of free radical production. This polymorphism is associated with several neurodegenerative disorders. We hypothesized that the 10398A allele is also associated with breast cancer susceptibility. African mitochondria harbor the 10398A allele less frequently than Caucasian mitochondria, which predominantly carry this allele. Mitochondrial genotypes at this locus were therefore determined in two separate populations of African-American women with invasive breast cancer and in controls. A preliminary study at Vanderbilt University (48 cases, 54 controls) uncovered an association between the 10398A allele and invasive breast cancer in African-American women, [odds ratio (OR), 2.90; 95% confidence interval (95% CI), 0.61-18.3; P = 0.11]. We subsequently validated this finding in a large, population-based, case-control study of breast cancer, the Carolina Breast Cancer Study at the University of North Carolina (654 cases, 605 controls). African-American women in this study with the 10398A allele had a significantly increased risk of invasive breast cancer (OR, 1.60; 95% CI, 1.10-2.31; P = 0.013). The 10398A allele remained an independent risk factor after adjustment for other well-accepted breast cancer risk factors. No association was detectable in white women (879 cases, 760 controls; OR, 1.03; 95% CI, 0.81-1.31; P = 0.81). This study provides novel epidemiologic evidence that the mtDNA 10398A allele influences breast cancer susceptibility in African-American women. mtDNA polymorphisms may be underappreciated factors in breast carcinogenesis.

The landscape of recombination in African Americans

Recombination, together with mutation, gives rise to genetic variation in populations. Here we leverage the recent mixture of people of African and European ancestry in the Americas to build a genetic map measuring the probability of crossing over at each position in the genome, based on about 2.1 million crossovers in 30,000 unrelated African Americans. At intervals of more than three megabases it is nearly identical to a map built in Europeans. At finer scales it differs significantly, and we identify about 2,500 recombination hotspots that are active in people of West African ancestry but nearly inactive in Europeans. The probability of a crossover at these hotspots is almost fully controlled by the alleles an individual carries at PRDM9 (P value < 10−245). We identify a 17-base-pair DNA sequence motif that is enriched in these hotspots, and is an excellent match to the predicted binding target of PRDM9 alleles common in West Africans and rare in Europeans. Sites of this motif are predicted to be risk loci for disease-causing genomic rearrangements in individuals carrying these alleles. More generally, this map provides a resource for research in human genetic variation and evolution.

Physical Activity and Postmenopausal Breast Cancer : Proposed Biologic Mechanisms and Areas for Future Research

Convincing evidence now supports a probable preventive role for physical activity in postmenopausal breast cancer. The mechanisms by which long-term physical activity affect risk, however, remain unclear. The aims of this review were to propose a biological model whereby long-term physical activity lowers postmenopausal breast cancer risk and to highlight gaps in the epidemiologic literature. To address the second aim, we summarized epidemiologic literature on 10 proposed biomarkers, namely, body mass index (BMI), estrogens, androgens, sex hormone binding globulin, leptin, adiponectin, markers of insulin resistance, tumor necrosis factor-α, interleukin-6, and C-reactive protein, in relation to postmenopausal breast cancer risk and physical activity, respectively. Associations were deemed “convincing,” “probable,” “possible,” or “hypothesized” using set criteria. Our proposed biological model illustrated the co-occurrence of overweight/obesity, insulin resistance, and chronic inflammation influencing cancer risk through interrelated mechanisms. The most convincing epidemiologic evidence supported associations between postmenopausal breast cancer risk and BMI, estrogens, and androgens, respectively. In relation to physical activity, associations were most convincing for BMI, estrone, insulin resistance, and C-reactive protein. Only BMI and estrone were convincingly (or probably) associated with both postmenopausal breast cancer risk and physical activity. There is a need for prospective cohort studies relating the proposed biomarkers to cancer risk and for long-term exercise randomized controlled trials comparing biomarker changes over time, specifically in postmenopausal women. Future etiologic studies should consider interactions among biomarkers, whereas exercise trials should explore exercise effects independently of weight loss, different exercise prescriptions, and effects on central adiposity. (Cancer Epidemiol Biomarkers Prev 2009;18(1):11–27)

The Carolina Breast Cancer Study: integrating population-based epidemiology and molecular biology

SummaryThe integration of epidemiology and molecular biology provides a new strategy to identify additional risk factors for breast cancer and to better understand the role played by traditionally recognized risk factors. The Carolina Breast Cancer Study (CBCS) is a population-based, case-control study designed to identify causes of breast cancer among Caucasian and African-American women who are residents of a 24-county area of central and eastern North Carolina. Information on established and potential breast cancer risk factors is obtained by personal interviews. Blood samples are collected from all consenting participants. Medical record documentation and paraffin-embedded tumor specimens are obtained for all breast cancer patients. DNA from tumor tissue is tested for a variety of molecular alterations characteristic of breast cancer. Germline DNA from blood lymphocytes is evaluated for presence of alleles increasing susceptibility to breast cancer. Statistical analyses evaluate gene-environment interaction by exploring the associations between environmental/behavioral factors and breast cancer in relation to specific molecular alterations (germline and tumor). Results will help identify high-risk women, clarify causal pathways, and hopefully contribute to the prevention of breast cancer.

Number of Nevi and Early-Life Ambient UV Exposure Are Associated with BRAF-Mutant Melanoma

Malignant melanomas often contain BRAF or NRAS mutations, but the relationship of these mutations to ambient UV exposure in combination with phenotypic characteristics is unknown. In a population-based case series from North Carolina, 214 first primary invasive melanoma patients in the year 2000 were interviewed regarding their risk factors. Ambient solar UV exposures were estimated using residential histories and a satellite-based model. Cases were grouped on the basis of BRAF and NRAS somatic mutations, determined using single-strand conformation polymorphism analysis and radiolabeled DNA sequencing, and the risk profiles of these groups were compared. Mutually exclusive BRAF-mutant and NRAS-mutant cases occurred at frequencies of 43.0% and 13.6% with mean ages at diagnosis of 47.3 and 62.1 years, respectively. Tumors from patients with >14 back nevi were more likely to harbor either a BRAF mutation [age-adjusted odds ratio (OR), 3.2; 95% confidence interval (95% CI), 1.4-7.0] or an NRAS mutation (age-adjusted OR, 1.7; 95% CI, 0.6-4.8) compared with patients with 0 to 4 back nevi. However, BRAF-mutant and NRAS-mutant tumors were distinctive in that BRAF-mutant tumors were characteristic of patients with high early-life ambient UV exposure (adjusted OR, 2.6; 95% CI, 1.2-5.3). When ambient UV irradiance was analyzed by decadal age, high exposure at ages 0 to 20 years was associated with BRAF-mutant cases, whereas high exposure at ages 50 and 60 years was characteristic of NRAS-mutant cases. Our results suggest that although nevus propensity is important for the occurrence of both BRAF and NRAS-mutant melanomas, ambient UV irradiance influences risk differently based on the age of exposure. The association of BRAF mutations with early-life UV exposure provides evidence in support of childhood sun protection for melanoma prevention. (Cancer Epidemiol Biomarkers Prev 2007;16(5):991–7)

Association between low levels of 1,25-dihydroxyvitamin D and breast cancer risk

OBJECTIVE To determine if blood levels of 25-hydroxyvitamin D (25-D) or its active metabolite, 1,25-dihydroxyvitamin D (1,25-D), are lower in women at the time of first diagnosis of breast cancer than in comparable women without breast cancer. DESIGN This was a clinic-based case-control study with controls frequency-matched to cases on race, age, clinic and month of blood drawing. SETTING University-based breast referral clinics. SUBJECTS One hundred and fifty-six women with histologically documented adenocarcinoma of the breast and 184 breast clinic controls. RESULTS There were significant mean differences in 1,25-D levels (pmol ml(-1)) between breast cancer cases and controls; white cases had lower 1,25-D levels than white controls (mean difference +/-SE: -11.08+/-0.76), and black cases had higher 1.25-D levels than black controls (mean difference +/-SE: 4.54+/-2.14), although the number of black women in the study was small. After adjustment for age, assay batch, month of blood draw, clinic and sample storage time, the odds ratio (95% confidence interval, CI) for lowest relative to highest quartile was 5.2 (95% CI 2.1, 12.8) for white cases and controls. The association in white women was stronger in women above the median age of 54 than in younger women, 4.7 (95% CI 2.1, 10.2) vs. 1.5 (95% CI 0.7, 3.0). There were no case-control differences in 25-D levels in either group. CONCLUSIONS These data are consistent with a protective effect of 1,25-D for breast cancer in white women.

High focal adhesion kinase expression in invasive breast carcinomas is associated with an aggressive phenotype

Focal adhesion kinase (FAK) is a protein tyrosine kinase expressed in invasive breast cancer that regulates antiapoptotic signaling. We have examined FAK expression by immunohistochemistry using anti-FAK 4.47 in breast tumor samples from a large population-based, case–control study of women participating in the University of North Carolina Breast Specialized Programs of Research Excellence (SPORE), Carolina Breast Cancer Study. In this population, 629 formalin-fixed, paraffin-embedded tissue sections were stained for FAK and scored as high (3+ or 4+ intensity and ≥90% positive cells) or otherwise. High FAK expression was associated with poor prognostic indicators including high mitotic index (>10 mitoses per 10 consecutive high-power fields), nuclear grade 3, architectural grade 3, estrogen and progesterone receptor negative, and HER-2/neu overexpressed using CB11 antibody. The association of high FAK expression with HER-2/neu overexpression lends further support that HER-2/neu and FAK collaborate to promote tumorigenesis. The presence of strong FAK expression in many high grade, estrogen- and progesterone-negative breast carcinomas indicates that FAK may be an attractive target for therapeutic intervention.

CA IX is an Independent Prognostic Marker in Premenopausal Breast Cancer Patients with One to Three Positive Lymph Nodes and a Putative Marker of Radiation Resistance

Purpose: Hypoxia in breast cancer is associated with poor prognosis and down-regulation of the estrogen receptor. Carbonic anhydrase IX (CA IX) is a hypoxia-inducible gene that has been associated with poor outcome in many epithelial cancers. Previous studies of CA IX in breast cancer have been carried out on mixed cohorts of premenopausal and postmenopausal patients with locally advanced disease and varying treatment regimens. We examined the potential prognostic and predictive role of CA IX in premenopausal breast cancer patients. Experimental Design: Using tissue microarrays, we analyzed CA IX expression in 400 stage II breast cancers from premenopausal women. The patients had previously participated in a randomized control trial comparing 2 years of tamoxifen to no systemic adjuvant treatment. Median follow-up was 13.9 years. Results: CA IX expression correlated positively with tumor size, grade, hypoxia-inducible factor 1α, Ki-67, cyclin E, and cyclin A2 expression. CA IX expression correlated negatively with cyclin D1, estrogen receptor, and progesterone receptor. CA IX expression was associated with a reduced relapse-free survival (P = 0.032), overall survival (P = 0.022), and breast cancer–specific survival (P = 0.005). Multivariate analysis revealed that CA IX was an independent prognostic marker in untreated patients with one to three positive lymph nodes (hazard ratio, 3.2; 95% confidence interval, 1.15-9.13; P = 0.027). Conclusion: CA IX is marker of poor prognosis in premenopausal breast cancer patients and it is an independent predictor of survival in patients with one to three positive lymph nodes. As all these patients received locoregional radiation therapy, CA IX may be associated with resistance to radiotherapy.