1. Finding a Genetic Link Among Women with
Triple Negative Breast Cancer
Nuria Astrid Perez Varela and Leticia Márquez-Magaña, PhD
Health Equity Research Lab, Department of Biology, San Francisco State University
ABSTRACT
EXPERIMENTAL DESIGN
Acknowledgements
EXPECTED RESULTS
FIGURE 1: African American and Latina women have the highest incidence
of TNBC in the United States.
We expect that all, or more than expected by random probability, of the
TNBC samples that are studied will have genetic ancestry that is African.
Expected Ancestral Lineage of TNBC Patients
Funding for this pilot comes from the California State University Program for
Education and Research in Biotechnology (CSUPERB) Entrepreneurial Joint Venture
Program. Ms. Perez-Varela was also supported by an NSF REU fellowship from SF
State University.
We thank Mr. Angel Ku for help in technical aspects of the project, and for continuing
with the work.
• Amplify, sequence, and determine mtDNA type of remaining samples.
• Determining the genetic ancestry of women inform future efforts to
develop molecular diagnostic tools and begin to unravel the genetics of
TNBC.
The specific objective of the pilot study is to identify the mtDNA type of
100 latina women with and without triple-negative breast cancer to
determine if an ancestral link exists among patients diagnosed with this
form of cancer.
OBJECTIVE
100 DNA samples collected from Latinas with
and without TNBC were obtained from
University of California, San Francisco.
- 31 with TNBC
- 34 with Triple positive BC
- 35 Healthy controls
Latinas were used for this study because
they are a heterogeneous, admixed
population group comprised of African,
European, and Native American ancestries.
Samples collected from Latinas with TNBC were matched to samples
obtained from women with Triple positive breast cancer, and to healthy
controls according to age, and reported self and parental origin as in the
following table.
FIGURE 6: mtDNA ancestry of TNBC samples from U.S. populations are
expected to be from the L1, L2 or L3 population groups (African Ancestry)
Human Migration and TNBC Rates
FIGURE 2: Limited studies of global TNBC distribution suggest African ancestry
for women afflicted with this disease.
Triple negative breast cancers (TNBC) are characterized by the absence of
estrogen receptor, progesterone receptor, and HER-2 expression making
them especially deadly. This is because these receptors are the targets for
highly successful treatments for breast cancer, and their absence makes it
difficult to treat TNBC. TNBC is found in 15% of U.S. women with breast
cancer,with African-American women having the highest incidence
(Figure 1). In sub-Saharan Africa the rate of TNBC appears to be much
higher. A recent study of 75 breast cancer patients in Ghana found that
82% had TNBC. The high rates of TNBC in African American and Ghanaian
women suggest it may have a genetic ancestral component. The purpose
of this study is to determine the mtDNA type of 100 Latinas with and
without TNBC to determine if an ancestral link exists among patients
diagnosed with this form of cancer. Latinas are a heterogeneous human
sub-population having European, Native American, and African ancestry.
The ancestral nature of their maternal lineage can be determined by
mtDNA typing. Therefore the mtDNA type of 31 latinas with TNBC, 34
with triple positive breast cancer, and 35 unaffected controls will be
determined. Preliminary results show that a TNBC cell line has a mtDNA
type indicative of African ancestry; whereas, a triple-positive cell line has
a mtDNA type indicative of European ancestry. Consequently, we predict
that TNBC samples will display greater percentage of African ancestry.
The identification of an ancestral link among women with TNBC may
allow for development of methods for its early detection and treatment.
Human (maternal) ancestry was identified by mtDNA typing. Specifically,
the mtDNA region known as the Hypervariable Region 1 (HVR1), that
contains 440 base pairs, was amplified and sequenced to identify the
genetic ancestry of Latinas with and without TNBC.
Age (years) Self origin Mother's origin Father's origin Cancer status
48 El Salvador El Salvador El Salvador Triple negative
49 El Salvador El Salvador El Salvador Triple positive
50 El Salvador El Salvador El Salvador Healthy
FIGURE 3: Latinas are a
heterogeneous sub-population
Ladder HVR 1
BP
1000
440
100
ladder (-) + + P P P H H H
FIGURE 4: HVR-1 Region
FIGURE 5: Agarose gel electrophoresis of
first six amplifications of mtDNA.
Sample # SNPs (C16223T indicates substitution of C at position 16223
in reference sequence with T in sample analyzed)
Haplogroup
(mtDNA
type)
Cancer Status
P14 C16223T A16235G C16278T C16294T
A16309G
L2 Triple positive
P22 16111T 16129A 16185G 16223T 16234T
16290T 16319G 16363C
A Triple positive
P24 T16032G A16151C A16154C A16170C
A16191T A16249C C16323T C16378T T16411C
H Triple positive
RESULTS
HVR-1 sequence was confirmed for three samples, and single nucleotide
polymorphisms (SNPs) were identified using Chromas Lite. The identified SNPs
were used to determine the mtDNA type (haplogroup) using The Genographic
Project, Haplogroup Prediction Tool.
The amplified and sequenced HVR-1 region of each sample was compared
to the Cambridge Reference Sequence (CRS), the first mitochondrial DNA
sequence published in 1987 and belonging to haplogroup H. This is a
mtDNA type prevalent in European populations.
FUTURE DIRECTIONS AND IMPACT OF WORK
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