There are well-established disparities in cancer incidence and outcomes by race/ethnicity that result from the interplay between structural, socioeconomic, socio-environmental, behavioural and biological factors. However, large research studies designed to investigate factors contributing to cancer aetiology and progression have mainly focused on populations of European origin. The limitations in clinicopathological and genetic data, as well as the reduced availability of biospecimens from diverse populations, contribute to the knowledge gap and have the potential to widen cancer health disparities. In this review, we summarise reported disparities and associated factors in the United States of America (USA) for the most common cancers (breast, prostate, lung and colon), and for a subset of other cancers that highlight the complexity of disparities (gastric, liver, pancreas and leukaemia). We focus on populations commonly identified and referred to as racial/ethnic minorities in the USA—African Americans/Blacks, American Indians and Alaska Natives, Asians, Native Hawaiians/other Pacific Islanders and Hispanics/Latinos. We conclude that even though substantial progress has been made in understanding the factors underlying cancer health disparities, marked inequities persist. Additional efforts are needed to include participants from diverse populations in the research of cancer aetiology, biology and treatment. Furthermore, to eliminate cancer health disparities, it will be necessary to facilitate access to, and utilisation of, health services to all individuals, and to address structural inequities, including racism, that disproportionally affect racial/ethnic minorities in the USA.

Genome-wide association studies (GWAS) of breast cancer defined by hormone receptor status have revealed loci contributing to susceptibility of estrogen receptor (ER)-negative subtypes. To identify additional genetic variants for ER-negative breast cancer, we conducted the largest meta-analysis of ER-negative disease to date, comprising 4754 ER-negative cases and 31 663 controls from three GWAS: NCI Breast and Prostate Cancer Cohort Consortium (BPC3) (2188 ER-negative cases; 25 519 controls of European ancestry), Triple Negative Breast Cancer Consortium (TNBCC) (1562 triple negative cases; 3399 controls of European ancestry) and African American Breast Cancer Consortium (AABC) (1004 ER-negative cases; 2745 controls). We performed in silico replication of 86 SNPs at P ≤ 1 × 10(-5) in an additional 11 209 breast cancer cases (946 with ER-negative disease) and 16 057 controls of Japanese, Latino and European ancestry. We identified two novel loci for breast cancer at 20q11 and 6q14. SNP rs2284378 at 20q11 was associated with ER-negative breast cancer (combined two-stage OR = 1.16; P = 1.1 × 10(-8)) but showed a weaker association with overall breast cancer (OR = 1.08, P = 1.3 × 10(-6)) based on 17 869 cases and 43 745 controls and no association with ER-positive disease (OR = 1.01, P = 0.67) based on 9965 cases and 22 902 controls. Similarly, rs17530068 at 6q14 was associated with breast cancer (OR = 1.12; P = 1.1 × 10(-9)), and with both ER-positive (OR = 1.09; P = 1.5 × 10(-5)) and ER-negative (OR = 1.16, P = 2.5 × 10(-7)) disease. We also confirmed three known loci associated with ER-negative (19p13) and both ER-negative and ER-positive breast cancer (6q25 and 12p11). Our results highlight the value of large-scale collaborative studies to identify novel breast cancer risk loci.

The population of Argentina is the result of the intermixing between several groups, including Indigenous American, European and African populations. Despite the commonly held idea that the population of Argentina is of mostly European origin, multiple studies have shown that this process of admixture had an impact in the entire Argentine population. In the present study we characterized the distribution of Indigenous American, European and African ancestry among individuals from different regions of Argentina and evaluated the level of discrepancy between self-reported grandparental origin and genetic ancestry estimates. A set of 99 autosomal ancestry informative markers (AIMs) was genotyped in a sample of 441 Argentine individuals to estimate genetic ancestry. We used non-parametric tests to evaluate statistical significance. The average ancestry for the Argentine sample overall was 65% European (95%CI: 63–68%), 31% Indigenous American (28–33%) and 4% African (3–4%). We observed statistically significant differences in European ancestry across Argentine regions [Buenos Aires province (BA) 76%, 95%CI: 73–79%; Northeast (NEA) 54%, 95%CI: 49–58%; Northwest (NWA) 33%, 95%CI: 21–41%; South 54%, 95%CI: 49–59%; p<0.0001] as well as between the capital and immediate suburbs of Buenos Aires city compared to more distant suburbs [80% (95%CI: 75–86%) versus 68% (95%CI: 58–77%), p = 0.01]. European ancestry among individuals that declared all grandparents born in Europe was 91% (95%CI: 88–94%) compared to 54% (95%CI: 51–57%) among those with no European grandparents (p<0.001). Our results demonstrate the range of variation in genetic ancestry among Argentine individuals from different regions in the country, highlighting the importance of taking this variation into account in genetic association and admixture mapping studies in this population.

U.S. Latinas have a lower incidence of breast cancer compared with non-Latina White women. This difference is partially explained by differences in the prevalence of known risk factors. Genetic factors may also contribute to this difference in incidence. Latinas are an admixed population with most of their genetic ancestry from Europeans and Indigenous Americans. We used genetic markers to estimate the ancestry of Latina breast cancer cases and controls and assessed the association with genetic ancestry, adjusting for reproductive and other risk factors. We typed a set of 106 ancestry informative markers in 440 Latina women with breast cancer and 597 Latina controls from the San Francisco Bay area and estimated genetic ancestry using a maximum likelihood method. Odds ratios (OR) and 95% confidence intervals (95% CI) for ancestry modeled as a continuous variable were estimated using logistic regression with known risk factors included as covariates. Higher European ancestry was associated with increased breast cancer risk. The OR for a 25% increase in European ancestry was 1.79 (95% CI, 1.28-2.79; P < 0.001). When known risk factors and place of birth were adjusted for, the association with European ancestry was attenuated but remained statistically significant (OR, 1.39; 95% CI, 1.06-2.11; P = 0.013). Further work is needed to determine if the association is due to genetic differences between populations or possibly due to environmental factors not measured. [Cancer Res 2008;68(23):9723-8]

The genetic contributions to breast cancer development among Latinas are not well understood. Here, we carry out a genome-wide association study of breast cancer in Latinas and identify a genome-wide significant risk variant, located 5’ of the Estrogen Receptor 1 gene (ESR1) (6q25 region). The minor allele for this variant is strongly protective (rs140068132: OR 0.60, 95%CI 0.53-0.67, P=9×10−18), originates from Indigenous Americans, and is uncorrelated with previously reported risk variants at 6q25. The association is stronger for estrogen receptor negative disease (OR 0.34 95% CI 0.21-0.54) than estrogen receptor positive disease (OR 0.63 95% CI 0.49-0.80) (P heterogeneity=0.01) and is also associated with mammographic breast density, a strong risk factor for breast cancer (P=0.001). rs140068132 is located within several transcription factor binding sites and electrophoretic mobility shift assays with MCF-7 nuclear protein demonstrate differential binding of the G/A alleles at this locus. These results highlight the importance of conducting research in diverse populations.

The incidence of breast cancer is 35% lower in Hispanic women living in the San Francisco Bay Area than in non-Hispanic White women. We have previously described a significant association between genetic ancestry and risk for breast cancer in a sample of U.S. Hispanics/Latinas. We retested the association in women residing in Mexico because of the possibility that the original finding may be confounded by U.S. specific unmeasured environmental exposures. We genotyped a set of 106 ancestry informative markers in 846 Mexican women with breast cancer and 1,035 unaffected controls and estimated genetic ancestry using a maximum likelihood method. Odds ratios and 95% confidence intervals (95% CI) for ancestry modeled as a categorical and continuous variable were estimated using logistic regression and adjusted for reproductive and other known risk factors. Greater European ancestry was associated with increased breast cancer risk in this new and independent sample of Mexican women residing in Mexico. Compared with women with 0% to 25% European ancestry, the risk was increased for women with 51% to 75% and 76% to 100% European ancestry [odds ratios, 1.35 (95% CI, 0.96-1.91) and 2.44 (95% CI, 0.94-6.35), respectively; P for trend = 0.044]. For every 25% increase in European ancestry (modeled as a continuous variable), there was a 20% increase in risk for breast cancer (95% CI, 1.03-1.41; P = 0.019). These results suggest that nongenetic factors play a crucial role in explaining the difference in breast cancer incidence between Latinas and non-Latina White women, and it also points out to the possibility of a genetic component to this difference.

Contemporary genetic variation among Latin Americans human groups reflects population migrations shaped by complex historical, social and economic factors. Consequently, admixture patterns may vary by geographic regions ranging from countries to neighborhoods. We examined the geographic variation of admixture across the island of Puerto Rico and the degree to which it could be explained by historic and social events. We analyzed a census-based sample of 642 Puerto Rican individuals that were genotyped for 93 ancestry informative markers (AIMs) to estimate African, European and Native American ancestry. Socioeconomic status (SES) data and geographic location were obtained for each individual. There was significant geographic variation of ancestry across the island. In particular, African ancestry demonstrated a decreasing East to West gradient that was partially explained by historical factors linked to the colonial sugar plantation system. SES also demonstrated a parallel decreasing cline from East to West. However, at a local level, SES and African ancestry were negatively correlated. European ancestry was strongly negatively correlated with African ancestry and therefore showed patterns complementary to African ancestry. By contrast, Native American ancestry showed little variation across the island and across individuals and appears to have played little social role historically. The observed geographic distributions of SES and genetic variation relate to historical social events and mating patterns, and have substantial implications for the design of studies in the recently admixed Puerto Rican population. More generally, our results demonstrate the importance of incorporating social and geographic data with genetics when studying contemporary admixed populations.

The prevalence of obesity (body mass index (BMI) ≥30 kg/m2) is higher in African Americans than in European Americans, even after adjustment for socioeconomic factors, suggesting that genetic factors may explain some of the difference. To identify genetic loci influencing BMI, we carried out a pooled analysis of genome-wide admixture mapping scans in 15,280 African Americans from 14 epidemiologic studies. Samples were genotyped at a median of 1,411 ancestry-informative markers. After adjusting for age, sex, and study, BMI was analyzed both as a dichotomized (top 20% versus bottom 20%) and a continuous trait. We found that a higher percentage of European ancestry was significantly correlated with lower BMI (ρ = −0.042, P = 1.6×10−7). In the dichotomized analysis, we detected two loci on chromosome X as associated with increased African ancestry: the first at Xq25 (locus-specific LOD = 5.94; genome-wide score = 3.22; case-control Z = −3.94); and the second at Xq13.1 (locus-specific LOD = 2.22; case-control Z = −4.62). Quantitative analysis identified a third locus at 5q13.3 where higher BMI was highly significantly associated with greater European ancestry (locus-specific LOD = 6.27; genome-wide score = 3.46). Further mapping studies with dense sets of markers will be necessary to identify the alleles in these regions of chromosomes X and 5 that may be associated with variation in BMI.