Vol.2, No.9, 1040-1048 (2010) Health
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Comparative study of breast cancer in Mexican and
Mexican-American women
María Elena Martínez1*, Luis Enrique Gutiérrez-Millan2, Melissa Bondy3,
Adrian Daneri-Navarro4, María Mercedes Meza-Montenegro5, Ivan Anduro-Corona2,
Ma Isabel Aramburo-Rubio6, Luz María Adriana Balderas-Peña7,
José Adelfo Barragan-Ruiz7, Abenaa Brewster3, Graciela Caire-Juvera8,
Juan Manuel Castro-Cervantes7, Mario Alberto Chávez Zamudio9, Giovanna Cruz1,
Alicia Del Toro-Arreola4, Mary E. Edgerton3, María Rosa Flores-Marquez7,
Ramon Antonio Franco-Topete10, Helga Garcia5, Susan Andrea Gutierrez-Rubio4,
Karin Hahn3, Luz Margarita Jimenez-Perez11, Ian K. Komenaka12, Zoila Arelí López Bujanda2,
Dihui Lu13, Gilberto Morgan-Villela7, James L. Murray3, Jesse N. Nodora14,
Antonio Oceguera-Villanueva15, Miguel Angel Ortiz Martínez13, Laura Pérez Michel13,
Antonio Quintero-Ramos9, Aysegul Sahin3, Jeong Yun Shim3, Maureen Stewart3,
Gonzalo Vazquez-Camacho7, Betsy Wertheim1, Rachel Zenuk1, Patricia Thompson1
1Arizona Cancer Center and Mel and Enid Zuckerman College of Public Health, University of Arizona, Tucson, USA;
*Corresponding Author: emartinez@azcc.arizona.edu
2Departamento de Investigaciones Científicas y Tecnológicas, Universidad de Sonora, Hermosillo, México
3University of Texas M.D. Anderson Cancer Center, Houston, USA
4Departamento de Fisiología, Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Guadalajara, México
5Instituto Tecnológico de Sonora, Ciudad Obregón, México
6Instituto Mexicano del Seguro Social, Hermosillo, México
7Instituto Mexicano del Seguro Social, CMNO, Guadalajara, Jalisco
8Centro de Investigación en Alimentación y Desarrollo, Hermosillo, México
9Instituto Mexicano del Seguro Social, Ciudad Obregón, México
10OPD Hospital Civil de Guadalajara, Guadalajara, México
11Departamento de Salud Pública, Centro Universitario de Ciencias de la Salud, Universidad de Guadalajara, Guadalajara, México
12Maricopa Medical Center, Department of Surgery, Phoenix, USA
13University of North Carolina, Lineberger Cancer Center, Chapel Hill, USA
14Arizona Cancer Center and Department of Family and Community Medicine, University of Arizona, Tucson, USA
15Instituto Jalisciense de Cancerología, Guadalajara, México
Received 25 March 2010; revised 5 May 2010; accepted 7 May 2010.
Breast cancer is the number one cause of can-
cer deaths among Hispanic women in the United
States, and in Mexico, it recently became the
primary cause of cancer deaths. This malign-
nancy represents a poorly understood and un-
derstudied disease in Hispanic women. The
ELLA Binational Breast Cancer Study was es-
tablished in 2006 as a multi-center study to as-
sess patterns of breast tumor markers, clinical
characteristics, and their risk factors in women
of Mexican descent. We describe the design and
implementation of the ELLA Study and provide a
risk factor comparison between women in the
U.S. and those in Mexico based on a sample of
765 patients (364 in the U.S. and 401 in Mexico).
Compared to women in Mexico, U.S. women had
significantly (p < 0.05) lower parity (3.2 vs. 3.9
mean live births) and breastfeeding rates (57.5%
vs. 80.5%), higher use of oral contraceptives
(60.7% vs. 50.1%) and hormone replacement
therapy (23.3% vs. 7.6%), and higher family
history of breast cancer (15.7% vs. 9.0%). Re-
sults show that differences in breast cancer risk
factor patterns exist between Mexico and U.S.
women. We provide lessons learned from the
conduct of our study. Binational studies are an
important step in understanding disease pat-
terns and etiology for women in both countries.
M. E. Martínez et al. / HEALTH 2 (2010) 1040-1048
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Keywords: Binational Study; Breast Cancer;
Hispanics; Mexico; United States
Rates of breast cancer in more developed nations have in
the past exceeded those in lower-income countries by a
factor of five or more [1]. In Mexico, the breast cancer
mortality rate has increased by 84% over the last two
decades [2,3] and it is now the most commonly diagnosed
cancer among women in Mexico [3]. In the United States
(U.S.), age-adjusted breast cancer incidence differs sig-
nificantly among racial/ethnic groups; rates are higher
among non-Hispanic whites (NHWs) and lower among
racial/ethnic minorities, including Hispanics [4]. Despite
their lower breast cancer incidence rates, Hispanic women
are 22% more likely to die of this disease [5]. Published
data [6-10], including our own studies in Arizona [11],
indicate that Hispanic women present with breast cancer
at an earlier age and with larger, more advanced stage
disease of higher grade, a profile similar to that observed
for African-American women. Relative to other racial/
ethnic groups, few epidemiological studies that focus on
breast cancer in Hispanic women have been conducted
to date. Published reports have provided data on the role
of reproductive factors [12,13], body size and obesity
[14], physical activity [15,16], contraceptive use [12,17],
diet [18], family history [13], and migration history [12,
19], in relation to breast cancer risk in Hispanic women
in the U.S.
It is now generally accepted that breast tumors exhibit
heterogeneity derived from intrinsic molecular differ-
ences that influence their natural history and response to
treatment [20]. A number of studies have shown that
steroid hormone dependent tumors differ with respect to
their biology and their risk factors [21] and that these
differences are clinically relevant in terms of treatment
selection, response, and patient prognosis [22-24]. In
spite of the importance of characterization of breast
cancer disease subtypes, no published data exist on the
prevalence of the tumor subtypes, such as luminal and
basal-like breast tumors in Hispanic women in the U.S.
Results of the few population-based studies published to
date [25-27], including our own [11], suggest that His-
panic women with breast cancer are more likely to be
diagnosed with hormone receptor negative tumors and
those that do not express human epidermal growth factor
receptor 2 (HER2), compared to NHWs [28,29].
Reasons for breast cancer disparities in Hispanic women
likely result from a combination of factors including
poor access to health care, less use of mammography
screening, genetic susceptibility, and environmental or
cultural factors. While there is increasing scrutiny of the
validity and theoretical basis of acculturation measures
[30-32], adequate and nuanced measurement of accultu-
ration could allow for the identification of variables
linked to risk-enhancing or protective behaviors associa-
ted with breast cancer and its subtypes.
The ELLA Binational Breast Cancer Study (hereafter
referred to as the ELLA Study) was established to
compare risk factor patterns, disease phenotypes, and
clinical characteristics between the U.S. and Mexico
populations. We hypothesized that the distribution of
breast tumor subsets differs between women in Mexico
and Mexican-American women residing in the U.S. and
that these differences are related to reproductive and
lifestyle factor profiles indicative of U.S. lifestyle and
cultural influences. Here we describe the design and
implementation of this binational study and provide a
comparison of risk factor characteristics between the two
2.1. Study Design and Recruitment
The ELLA Study was initiated in 2006 as a pilot effort
with the formation of a binational investigative team,
comprising three sites in Mexico (Universidad de Gua-
dalajara in Guadalajara, Jalisco; Universidad de Sonora
in Hermosillo, Sonora; and Instituto Tecnológico de
Sonora in Ciudad Obregón, Sonora) and two sites in the
U.S. (Arizona Cancer Center, in Tucson, Arizona, which
included recruitment sites throughout the state; and at
the University of Texas M.D. Anderson Cancer Center in
Houston, Texas, which included two additional recruit-
ment sites) (See Table 1). An essential component of the
ELLA study was the partnership with clinicians and
pathologists from health care settings serving the study
participants both in Mexico and the U.S. Health care
providers included those from Mexico’s nationalized
health care system: the Instituto Mexicano del Seguro
Social (IMSS) in all three sites and the Hospital Civil
and Instituto Jaliscience de Cancerología in Guadalajara.
The study was approved by the respective Institutional
Review Boards, including the IMSS. Written informed
consent was obtained for all participants.
Participants were eligible if they were diagnosed
within 24 months of recruitment with invasive breast
cancer and were 18 years of age or older. In the U.S., par-
ticipants were self-identified as being of Mexican descent.
Women with carcinoma in situ and those with recurrent
disease were ineligible. A clinic-based approach was the
dominant strategy used for recruitment in the study,
although the number of recruitment sites and their tactics
M. E. Martínez et al. / HEALTH 2 (2010) 1041-1048
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of identifying patients differed by region (see Table 1).
2.2. Data Collection
Participation involved in-person (93%) or telephone ad-
ministration (7%) of a risk factor questionnaire. Three
comparable questionnaires were created: English and
Spanish versions for the U.S. and a separate instrument
for Mexico. No differences existed between the two U.S.
versions and only minor differences between the U.S.
and Mexico questionnaires (see Table 2).
All study personnel were jointly trained prior to the
initiation of recruitment and continue to receive training
as needed. The instrument takes a median of 45.0 min-
utes to administer (59.0 minutes for Mexico and 43.2
minutes for the U.S.).
As part of data collection, we abstracted the medical
records for clinical and histopathological factors, includ-
ing predictive and prognostic factors. It is important to
note that ER, PR, and HER2 are not uniformly con-
ducted in all IMSS institutions in Mexico; marker status
is not conducted at all in the Hospital Civil or the Insti-
tuto Jaliscience de Cancerología. The Avon Foundation,
one of the study’s sponsors, provided additional funding
for the breast cancer patients to have consistent tumor
marker information that is important for their treatment
Figure 1 presents the operational structure of the
ELLA Study. The organizational structure includes the
five recruitment sites, the research core elements, and
the Steering and Advisory Committees. Recruitment,
data collection, tissue collection, and DNA extraction are
conducted at each site.
2.3. Biological Samples
An essential component of the ELLA Study was the
routine collection of formalin fixed paraffin embedded
(FFPE) breast cancer tissue including biopsy sample for
patients receiving neoadjuvant therapy. FFPE tissue
samples were sent to M.D. Anderson Cancer Center for
the construction of tissue microarrays (TMAs) (Figure
1). The markers being evaluated in the TMAs were
selected to characterize basal and luminal subtypes (ER,
PR, and HER2, Ki67, epidermal growth factor receptor
(EGFR) and basal cytokeratins [CK5 or 6, CK14 and
CK17]) for subset delineation by immunohistochemistry
as described by Nielsen et al. [33]. Prior to initiation of
the ELLA recruitment, special trainings were conducted
at Ventana Medical Systems (Tucson, Arizona) that in-
cluded all Mexico pathologists involved in the study. To
assure uniformity of tumor marker measures of diagno-
stic value across community and international laborato-
ries, ER, PR, HER2, and Ki67 analyses were repeated on
all tumor samples at Ventana Medical Systems with auto-
mation and intra- and inter-batch control. We do not
present clinical characteristics or marker data due to their
premature nature as data derived from Mexico will need
to undergo quality control verification.
Figure 1 also shows the establishment of a deoxyribo-
nucleic acid (DNA) repository with the collection of
blood or saliva on all participants. DNA was extracted at
each recruitment site from saliva according to manufac-
turer instruction for the Oragene saliva kit (DNA Genotek©,
Ontario Canada) or from blood using the QIAmp Mini
Kit (Qiagen©, Valencia CA). A single DNA aliquot was
then sent to the Arizona Cancer Center for study banking
with each site retaining the remainder of their study
2.4. Data Management and Tissue Tracking
Data management supporting the risk factor question-
naire and medical record abstraction for the ELLA Study
was centralized at the Arizona Cancer Center. We de-
veloped web-based databases built with two well-establi-
shed open-source software systems, providing the capac-
ity to allow access from anywhere via the Internet. Da-
tabase applications were built around the individual needs
Table 1. Recruitment sites in the ELLA study, March 1, 2007 to June 1, 2009.
Region Recruitment Sites
Arizona (United States)
Arizona Cancer Center (Tucson); St. Elizabeth of Hungary Clinic (Tucson); University Physician’s
Healthcare Kino Hospital (Tucson); El Rio Community Health Center (Tucson); Arizona Oncology
(Tucson); Maricopa Integrated Health System (Phoenix); Mountain Park Community Health Center
(Phoenix); Dr. Edward Donahue (Phoenix); Arizona Oncology (Phoenix); Mariposa Community Health
Center (Nogales); Regional Center for Border Health (Yuma).
Houston, Texas (United States) M.D. Anderson Cancer Center; Lyndon B. Johnson Hospital; The Rose Diagnostic Clinic.
Guadalajara, Jalisco (Mexico) Instituto Mexicano del Seguro Social; OPD Hospital Civil de Guadalajara; Instituto Jaliscience de
Ciudad Obregon, Sonora (Mexico) Instituto Mexicano del Seguro Social.
Hermosillo, Sonora (Mexico) Instituto Mexicano del Seguro Social.
M. E. Martínez et al. / HEALTH 2 (2010) 1040-1048
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Table 2. Characteristics of the risk factor questionnaire and the medical record abstraction in the ELLA study.
Characteristic Details
Sociodemographics Date and place of birth, residence history, age at migration to the U.S. (U.S. only), education, marital status,
religious preference, income (Mexico only), parents’ place of birth, poverty index (Mexico only).
Occupational history Longest paid job held for one year or longer; farm work.
Pesticide exposure Exposure at home, residence in or near agricultural community.
Language use, media language exposure (U.S. only). Westernization questionnaire developed for Mexican pa-
Tobacco Exposure Cigarette use status (never, past, current), dose, and duration. Second-hand smoke exposure history.
Alcohol History Alcohol use, type, dose and duration.
Menstrual history Age at menarche, menstrual cycle regularity. Age at menopause and type.
Pregnancy history Age at pregnancy, number of full term pregnancies, type of birth, breast feeding, weight gain.
Breast health history History of breast self exam, clinical breast exam, mammography, biopsies.
Method of breast cancer detection, symptoms, delay in care, reason(s) for delay.
Medical history History of diabetes, hypertension, heart disease, endometriosis, autoimmune disease(s), polycystic ovaries, gall-
bladder disease, radiation to the chest.
Medication use Use of aspirin/nonsteroidal anti-inflammatory drugs and oral corticosteroids, dose, and duration.
Birth control and hormone
use Type of birth control and history of use. HRT use, type, and duration.
Family history of cancer First and second degree family members, type of cancer, and age at diagnosis of affected family member.
Physical activity Time spent in occupational, housework, and recreational activities and activity type. Sedentary behavior (time
spent sitting and sleeping). Activity level at various ages during lifetime.
Anthropometrics Height, weight, and weight history. Waist and hip measurement.
Medical Record abstraction Site of recruitment. Age at diagnosis. Stage, histology, tumor markers (ER, PR, HER2).
Abbreviations: ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; HRT, hormone replacement therapy; PR, progesterone receptor; U.S.,
United States
of the study and tailored to meet its specific tasks. With
Secured Socket Layer (SSL) certificate, the password
protected online database application was free of inter-
cept by others during data transmission from each study
site to the database server. We developed a tissue track-
ing database in Oracle (Oracle, Redwood Shores CA),
a relational database using caTissue Version 1.0 structure
with extensions to track tissue transfer across the ELLA
consortium (Figure 1). All bodily fluids and FFPE tissue
samples were inventoried in the ELLA Station and the
data are secure at the M.D. Anderson Cancer Center. The
database can be accessed via a browser-based front end
using Java Server Faces
Data presented are based on 765 study participants re-
cruited as of June 1, 2009 (364 in the U.S. and 401 in
Mexico). The majority (78.9%) of participants were in-
terviewed within one year of diagnosis. Response rates
were extremely high, ranging from 95 to 99%. Table 3
presents selected risk factor characteristics for the total
population as well as by country.
Women in the U.S. were significantly younger than
those in Mexico. Fifty-nine percent of the U.S. patients
were born in Mexico and the majority has lived in the
U.S. for over ten years. We recruited roughly equal pro-
portions of English and Spanish speakers in the U.S.
Women in Mexico had a significantly higher number of
live births and rates of breastfeeding. The proportion of
post-menopausal women was significantly higher in Me-
xico than the U.S. Use of oral contraceptives and hor-
mone replacement therapy were significantly higher in
the U.S. than Mexico, but use of hormone therapy was
low overall (14%). Women in Mexico were less likely to
have had prior mammography. Although obesity rates
were equally high in both countries, women in Mexico
reported a lower BMI at age 30 compared to those in the
U.S. Current cigarette smoking was low in both coun-
tries, whereas alcohol consumption was significantly
higher in the U.S. than in Mexico.
M. E. Martínez et al. / HEALTH 2 (2010) 1041-1048
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Advisory Committee
Steering Committee
Principal Investigators
MDACC University of Arizona
Universidad of SonoraUniversidad de GuadalajaraInstituto Tecnológico de Sonora
Tumor Tissue Collection
Collection at each site
TMA construction at MDACC
Sample Collection
Blood or Saliva
DNA Extraction at each site
IT/Data Management
Questionnaire and Medical Record Data
Web-based database housed at Arizona
Tumor Tissue DNA
Extraction and
Blood/Saliva DNA GenotypingStatistics
Figure 1. ELLA binational breast cancer study organizational structure. The organizational structure
includes the five recruitment sites, the research core elements, and the Steering and Advisory Com-
mittees. Recruitment, data collection, tissue collection, and DNA extraction are conducted at each
site. Tracking of participants, Risk Factor Questionnaire (RFQ), Medical Record Abstraction (MRA),
and biological samples (deoxyribonucleic acid [DNA] and Tissue Microarray [TMA] repositories)
are maintained in separate but integrated databases. Databases can be accessed via browser-based
front end using Secured Socket Layer certificate.
In 2006, there were 44.3 million Hispanics (14.8 percent
of total) in the U.S., with those of Mexican descent
comprising 64 percent of the total. It is projected that the
Hispanic population will grow to 102.6 million (24.4
percent of total) by 2050 [34], making it the fastest
growing racial/ethnic minority group in the U.S. In addi-
tion, foreign born individuals from Mexico comprise the
largest immigrant group in the U.S. In spite of the con-
tinued growth of the Hispanic population in the U.S.
(44.3 million in 2006) [34] and the fact that breast can-
cer represents the number one cause of cancer deaths in
Hispanic women [35], limited data exist on breast cancer
risk factors or the breast cancer clinical and tumor
marker profile for this underserved population.
The binational nature of the ELLA Study and re-
cruitment of large numbers of women of Mexican
descent in the U.S. and Mexico will provide a unique
opportunity to explore a variety of risk and protective
factors in relation to breast cancer subtypes, including
the cultural impact of the adoption of U.S. lifestyles.
Pike et al. [12] proposed that the lower breast cancer
risk among Hispanic women compared to NHWs is
almost entirely explained by their younger age at first
full term pregnancy, higher parity, low use of HRT,
and low alcohol consumption. These authors also ob-
served a lower risk of breast cancer in foreign-born
than U.S.-born Hispanics. The large proportion of
foreign-born women in the ELLA Study (59%) will
provide unique opportunities to assess residency and
migration history in relation to risk factor profiles and
disease patterns. Our data show that Mexican women
with breast cancer tend to have more children, are less
likely to use contraceptives or HRT, and less likely to
consume alcohol or smoke cigarettes, as compared to
their U.S. counterparts. However, no differences were
shown for age at menarche, age at menopause, or age
at first birth. Data from the South-west Hormone, In-
sulin, Nutrition, and Exercise (SHINE) Study [15,18]
show that a later age at menarche and higher parity
were shown to be protective, whereas a later age at
first birth was associated with higher risk of breast
cancer; however, associations were not all statistically
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Table 3. Characteristics of participants in the ELLA study, March 1, 2007 to June 1, 2009.
Total (N = 765) U.S. (N = 364) Mexico (N = 401)
Age at interview, years, mean (SD) 53.6 (12.6) 51.6 (12.2) 55.5 (12.7)*
Highest level of educationa, No. (%)
Less than high school 376 (53.3) 142 (39.1) 234 (68.4)
High school 187 (26.5) 120 (33.1) 67 (19.6)
Post-high school 142 (20.1) 101 (27.8) 41 (12.0)*
Country of birthb, No. (%)
U.S.-born 150 (41.2)
Foreign-born 214 (58.8)
Nativityb, No. (%)
U.S.-born, living in U.S. 10 y 137 (37.6)
U.S.-born, living in U.S. < 10 y 13 (3.6)
Foreign-born, living in US 10 y 163 (44.8)
Foreign-born, living in US < 10 y 51 (14.0)
Language useb,c, No. (%)
English 173 (47.5)
Spanish 191 (52.5)
Age at menarche (y), mean ± SD 12.8 (1.6) 12.8 (1.6) 12.9 (1.6)
Parous, No. (%) 700 (91.5) 334 (91.8) 366 (91.3)
Age at first live birth, mean (SD) 22.9 (5.5) 22.7 (5.6) 23.0 (5.5)
No. live births, mean (SD) 3.6 (2.1) 3.2 (1.8) 3.9 (2.4)*
Ever breastfeedingd, No. (%) 532 (69.6) 210 (57.7) 322 (80.5)*
Up to 9 months 165 (31.0) 87 (41.4) 78 (24.2)
9+ months 367 (69.0) 123 (58.6) 244 (75.8)*
Menopausal status at interview, No. (%)
Premenopausal 334 (43.7) 186 (51.1) 148 (36.7)*
Post-menopausale 431 (56.3) 178 (48.9) 253 (63.1)
Age at natural menopause, years, mean (SD) 48.4 (5.2) 48.7 (4.7) 48.3 (5.4)
Contraceptive usef, No. (%) 416 (55.2) 219 (60.7) 197 (50.1)*
HRT use g, No. (%) 70 (14.3) 49 (23.3) 21 (7.6)*
Prior mammography, No. (%) 470 (61.4) 244 (67.0) 226 (56.4)*
Family history of breast cancerh, No. (%) 91 (12.2) 56 (15.7) 35 (9.0)*
Recent BMIi, mean (SD) 29.2 (6.2) 29.6 (6.9) 28.8 (5.4)
Underweight (< 18.5), No. (%) 5 (0.8) 4 (1.2) 1 (0.3)
Normal (18.5-24.9), No. (%) 163 (24.6) 81 (24.7) 82 (24.6)
Overweight (25.0-29.9), No. (%) 232 (35.1) 105 (32.0) 127 (38.0)
Obese ( 30.0), No. (%) 262 (39.6) 138 (42.1) 124 (37.1)
BMI at age 30 yearsj, mean (SD) 24.4 (4.6) 24.7 (4.9) 24.0 (4.3)
Waist circumferencek, cm, mean (SD) 95.2 (14.2) 94.4 (16.6) 95.6 (12.8)
Waist/hip ratiol, cm, mean (SD) 0.88 (0.1) 0.88 (0.1) 0.89 (0.1)
Current cigarette smoking, No. (%) 50 (6.5) 29 (8.0) 21 (5.2)
Alcohol usem, No. (%) 428 (56.1) 228 (62.8) 200 (50.0)*
M. E. Martínez et al. / HEALTH 2 (2010) 1041-1048
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Abbreviations: BMI, body mass index; HRT, hormone replacement therapy; SD, standard deviation; U.S., United States; *P < 0.05 comparing differences
between Mexico and the U.S. Differences in means were determined by t test, and differences in proportions were determined by chi-squared tests; P val-
ues are 2 sided; aIncludes 705 participants (363 in the U.S. and 342 in Mexico); bAll Mexican women were born in Mexico had questionnaire administered
in Spanish. With the exception of 2 participants, all foreign-born U.S. women were born in Mexico; cBased on language use during the interview.; dIn-
cludes 764 participants (364 in the U.S. and 400 in Mexico); ePeriods stopped for at least 12 months due to natural menopause, bilateral oopherectomy, or
other reason and age at interview older than mean age of natural menopause; fIncludes 754 participants (361 in the U.S. and 393 in Mexico); gIncludes
women reporting periods stopped for at least 12 months; 488 participants (210 in the U.S. and 278 in Mexico); hFamily history of breast cancer in first de-
gree relatives. Excludes adopted women who reported not knowing their blood relatives and those who reported not knowing whether any family member
had any type of cancer. Includes 746 participants (356 in the U.S. and 390 in Mexico); iWeight (kg)/height (m)2. Defined by self-reported weight and
height 1-3 years prior to diagnosis. Includes 662 participants (328 in the U.S. and 334 in Mexico); jWeight (kg)/height (m)2. Includes 542 participants (296
in the U.S. and 246 in Mexico) and excludes women less than 30 years of age; kIncludes 603 participants (208 in the U.S. and 395 in Mexico); lIncludes
599 participants (207 in the U.S. and 392 in Mexico); mIncludes 763 participants (363 in the U.S. and 400 in Mexico).
significant, and some varied by pre- and post-menopausal
status. Data on the protective effect of breastfeeding have
been published, including the most recent recommenda-
tions from the World Cancer Research Fund/American
Institute for Cancer Research (WCRF/AICR) for breast
cancer prevention [36]. Given the high proportion of
women who breastfed in the ELLA Study (70%), future
studies will be able to explore associations among
women by molecular subtype with higher rates of breast-
feeding than those reported in the literature.
Our data on obesity show that prevalence is equally
high in both countries. Obesity in Mexico is a recent
major epidemic; in 1988, 33.4 % of adults were classi-
fied as overweight/obese and this figure has risen to
71.9% in 2006 [37], with rates higher in women than
men. In the U.S., Hispanics suffer disproportionately
from obesity [38], albeit foreign-born Hispanics have a
lower likelihood of being overweight/obese compared
with those born in the U.S. [39]. Although results of the
SHINE study showed no deleterious effect of obesity for
risk of breast cancer in pre- or post-menopausal Hispanic
women [15], a better understanding of its potential ef-
fects on the distribution of breast cancer specific pheno-
types is needed. Results of two studies found that a
higher BMI and/or a high waist-to-hip ratio was associ-
ated with an increased risk of basal-like breast cancer
[40,41] or triple negative tumors [42]. Data from the
ELLA study will allow us to elucidate the relation of
obesity measures to disease phenotypes for women of
Mexican descent who are disproportionately affected by
high rates of overweight and obesity.
Reports in the literature show that Hispanic women
tend to be diagnosed at a younger age than NHWs [6,
7,43]. Our data based on age at interview are consistent
with these findings. Whether or not this lower age pri-
marily reflects the age structure of the population is un-
clear. In the U.S, Hispanics have a lower median age
compared to NHWs (25.8 vs. 38.6 years) [34] and is
similar to the median age in Mexico (25 years) [44].
Data on tumor stage show that women in Mexico are
diagnosed less frequently with early stage tumors, which
is consistent with published reports from Mexico [45].
Results of our study show lower rates of mammography
screening in Mexican participants compared to those in
the U.S., albeit these are much higher than those re-
ported in national surveys for Mexico [46].
Limitations of our study include the lack of a popula-
tion-based sample. Both countries included largely a
clinic-based recruitment. Given that Mexico does not
have a population-based cancer registry, recruitment for
the study occurred in the IMSS hospitals in all three sites.
IMSS covers approximately 60% of the Mexican popu-
lation by providing care to all formally employed indi-
viduals and their family members. In Guadalajara, two
additional hospitals that serve the unemployed, poorer
segment of the population were used for recruitment.
Thus, in Mexico, patients seeking care in the private
hospital setting are not captured through our recruitment
strategies; however, this is likely to represent only ap-
proximately 5% of the population [47]. In the U.S., re-
cruitment took place at M.D. Anderson, a tertiary refer-
ral center, a county hospital, and a clinic serving indigent
patients and underserved women. In Arizona, cases were
ascertained at the Arizona Cancer Center, county hospi-
tals in Tucson and Phoenix, community health centers,
and other facilities that serve the Hispanic population in
the state.
Results of the ELLA Study show that differences exist
in breast cancer risk factor patterns between Mexico and
the U.S. women. Our experience working with Mexico
has shown that logistics related to recruitment, collection
of medical record data, and tissue retrieval is less chal-
lenging in this country compared to the U.S. Given that
our study includes well-characterized populations, with
comprehensive epidemiological data linked to well-anno-
tated tumor samples and clinical data, future studies will
be extremely valuable in understanding the breast cancer
burden in Mexican and Mexican-American women.
We are indebted to Ana Lilia Amador, Leticia Cordova, Carole Kepler,
and Fang Wang from the Arizona Cancer Center as well as Dr. Alejan-
dro Gómez-Alcalá from the IMSS in Ciudad Obregon, Sonora for their
valuable contribution. We appreciate the support of the Biosciences
Graduate Studies of the Department of Scientific and Technological
M. E. Martínez et al. / HEALTH 2 (2010) 1040-1048
Copyright © 2010 SciRes. Openly accessible at http://www.scirp.org/journal/HEALTH/
Research of the University of Sonora.
In the U.S., work was supported by the Avon Foundation, a supplement
to the Arizona Cancer Center Core Grant from the National Cancer
Institute (CA-023074-2953), a grant from Susan G. Komen for the
Cure (KG090934) and a supplement to the M.D. Anderson Cancer
Center SPORE in Breast Cancer (P50 CA116199-02S1). In Mexico,
work was supported by the Consejo Nacional de Ciencia y Tecnología
de México (CONACYT).
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