
Cancer Epidemiology Biomarkers & Prevention Vol. 10, 147-149, February 2001
© 2001 American Association for Cancer Research
Levels of 5-Hydroxymethyl-2'-deoxyuridine in DNA from Blood of Women Scheduled for Breast Biopsy1
Zora Djuric2,
Lance K. Heilbrun,
Samir Lababidi,
Egle Berzinkas,
Michael S. Simon and
Mary A. Kosir
Barbara Ann Karmanos Cancer Institute, Wayne State University, Detroit, Michigan 48201
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Abstract
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Systemic oxidative stress is thought to contribute to risk of various
cancers, including breast cancer. DNA repair ability also has been
associated with breast cancer risk. In this work, we examined levels of
oxidative DNA damage as an indication of breast cancer risk in women
because oxidative DNA damage levels should reflect the net balance of
oxidative stress and DNA repair ability. Levels of
5-hydroxymethyl-2'-deoxyuridine, one form of oxidative DNA
damage, were measured in DNA from blood of women scheduled for breast
biopsy. The blood samples analyzed included women whose biopsy results
indicated invasive breast cancer, high-risk lesions (atypical
hyperplasia or carcinoma in situ), or benign lesions.
Mean levels of 5-hydroxymethyl-2'-deoxyuridine were significantly
higher in blood of women who had high risk or invasive breast lesions
versus women with benign lesions. If atypical
hyperplasia or carcinoma in situ are precursor lesions
for breast cancer, then these results suggest that oxidative DNA damage
may be involved in the cancer process before invasive cancer develops.
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Introduction
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Systemic oxidative stress levels, as evidenced by DNA damage and
lipid oxidation products in blood and urine, appear to be associated
with increased risk of various cancers, including that of the breast
(1
, 2)
. DNA repair ability in blood lymphocytes also has
been shown to be related to breast cancer risk (3, 4, 5, 6)
.
Interestingly, individuals with BRCA1 or BRCA2 mutations may be
at increased cancer risk because of deficiencies in repair of DNA
lesions caused by oxygen free radicals (7)
. Oxidative DNA
damage is therefore an attractive marker of risk because it takes into
account not only exposure to and production of oxidants, but also DNA
repair ability.
Our previous data indicated that women with breast cancer have higher
levels of oxidative DNA damage in the blood than do control women
(1)
. That study, however, was performed using blood
obtained in a retrospective design with a convenience sample of
controls. We now present data from a prospective study: blood was
obtained from subjects prior to breast biopsy. This design resulted in
the enrollment of women with a variety of breast lesions, including
women who were at increased risk of breast cancer because of the
presence of atypical hyperplasia or carcinoma in situ. It
has been hypothesized that atypical hyperplasia and carcinoma in
situ are precursor lesions to invasive breast cancer (8
, 9)
. These types of lesions are known to increase a womans risk
of breast cancer substantially (10)
. It was therefore of
particular interest to include this group of women to help us
investigate
5-OHmdU3
as a marker of increased breast cancer risk.
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Materials and Methods
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Patients.
Women were recruited from the Karmanos Cancer Institute Comprehensive
Breast Clinic during the period October 1994 through January 1996. A
research assistant asked women who were scheduled for a biopsy whether
they would fill out a questionnaire and provide a blood sample for a
biomarker study. This occurred at a clinic visit that was typically
several days before the biopsy. Eligibility criteria were that subjects
be at least 18 years of age and had never had a previous diagnosis of
cancer. During this time period, a total of 252 subjects were enrolled.
Blood Samples.
Heparinized blood (10-ml) was used to prepare nuclei by the method of
Ciulla et al. (11)
. Nuclei were frozen at
-70°C in 50 mM mannitol, 1
mM EDTA, and 1% SDS until DNA could be
extracted. DNA was isolated from nuclei by a modification of the
procedure of Miller et al. (12)
. Briefly, the
nuclei were treated with RNases A and proteinase K. The proteins were
precipitated by the addition a one-third volume of 6
M sodium chloride, shaking, and centrifugation.
One extraction with chloroform-isoamyl alcohol (48:2, v/v) and
one extraction with n-butyl alcohol were used to remove
residual protein. The DNA was precipitated twice and dissolved in 200
µl of water, and a UV scan was obtained.
The isolated DNA (100150 µg) was hydrolyzed enzymatically and
derivatized, and 5-OHmdU levels were determined by gas
chromatography-mass spectrometry using isotopically labeled
internal standards as described previously (13)
. The
samples were derivatized with
N,O-bis(trimethylsilyl)trifluoroacetamide
containing 1% trimethylchlorosilane and acetonitrile (2:1,
v/v) by heating at 120°C for 20 min. Gas chromatographic
separations were performed with a 25-m Hewlett-Packard SE54 Ultra 2
column using helium as the carrier gas.
Statistical Analyses.
Simple descriptive statistics were used to summarize the baseline
demographic variables and levels of 5-OHmdU, by diagnosis category.
Spearmans rank correlation was used to assess the relationship
of continuous covariables and 5-OHmdU levels. Comparison of pre- and
postbiopsy 5-OHmdU levels (in a small subset of the women) was
performed using the nonparametric Wilcoxon signed-rank test for paired
data. Simultaneous comparison of 5-OHmdU distributions by diagnosis
group (and by other factors) relied on the k-sample
Kruskal-Wallis rank-sum test. All pairs of diagnosis groups were then
contrasted using a nonparametric multiple-comparisons procedure
(14)
. Despite age-matching of the subjects with benign
breast lesions, a significant correlation of age with levels of 5-OHmdU
remained. Thus, comparison of 5-OHmdU levels by diagnosis group, after
adjustment for age and smoking status, was performed via a two-way
analysis of covariance model (15)
, with age as a
continuous covariate. For this statistical modeling work, a double
natural log [ln(ln)] transformation was necessary to normalize the
5-OHmdU data. The adjusted means (and confidence limits) were
transformed back to the original scale of measurement to facilitate
results interpretation.
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Results
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Blood Samples.
A total of 252 subjects were enrolled. Of those, 225 were considered
analysis-eligible based on whether the blood was in fact drawn, whether
the biopsy was subsequently performed at our institution, and whether a
definitive pathology report was available. The samples included 131
biopsies that were considered benign (adenosis, apocrine or squamous
metaplasia, cysts, mild hyperplasia, duct ectasia, fibroadenoma,
mastitis) and 35 biopsies that are associated with a slightly increased
risk of breast cancer (moderate or florid hyperplasia, ductal papilloma
with fibrovascular core and sclerosing adenosis). The high-risk
biopsies included 15 with atypical hyperplasia, 9 with ductal carcinoma
in situ, and 3 with lobular carcinoma in
situ. The invasive cancers were 27 infiltrating ductal
carcinomas, 2 infiltrating lobular carcinomas, and 3 other cancers
(medullary, phyllodes, and a poorly differentiated carcinoma).
The blood samples analyzed were all those available for this study from
the high-risk and invasive groups: 22 of 27 subjects with biopsies in
the high-risk category (2 with lobular carcinoma in situ, 7
with ductal carcinoma in situ, and 13 with atypical
hyperplasia), and 23 of 29 in the invasive category (22 ductal and 1
lobular infiltrating cancer). Of the samples that were not available
for this study, three did not have pathology reports completed at the
time of sample analysis and the others did not have a tube of blood
available for this assay. There were also 28 age-matched subjects from
the benign category selected for analysis, but 1 of those samples
yielded insufficient DNA, which left 27 for analysis. The age matching
was done by first determining the age distribution, by decades, of the
subjects in the high-risk and invasive categories. This turned out to
be similar in each of those two groups. Subjects in the benign category
were then randomly selected to match this distribution (with one extra
subject for each age group), at the same time ensuring that samples
were evenly distributed from the early, mid, and late enrollment
periods.
Levels of 5-OHmdU.
We examined the association of 5-OHmdU with the following covariates:
age, race (Caucasian, African-American, Asian), body weight, smoking
status (current, past, never), menopausal status (pre-, peri-, or
postmenopause), first-degree family history of breast cancer or any
other nonaerodigestive cancer (yes/no), and other health problems
(cardiovascular/hypertension problem, diabetes, arthritis, asthma
versus none of these). Some of these factors are summarized
in Table 1
. The only significant associations with 5-OHmdU were with age (rank
correlation = 0.25; P = 0.033), and smoking status
(Kruskal-Wallis test, P = 0.031). Information on use of
medications, such as hormone replacement therapy, was not available and
is a potential limitation of this study.
The mean levels of 5-OHmdU in blood of women with either invasive
cancer or high-risk lesions were significantly higher than in women
with benign lesions (Table 2)
. After adjustment for age and smoking status, the results were similar
to the unadjusted results (see Table 2
). The adjusted mean 5-OHmdU of
women with benign lesions was significantly lower than that of women in
either of the other two diagnosis groups. The high-risk and invasive
cancer groups again were not statistically significantly different.
Interestingly, the distribution of 5-OHmdU levels across quintiles was
such that the women with high-risk lesions exhibited levels only in the
upper three quintiles, whereas women in the other two groups were
distributed across all five quintiles. The numbers of women in each
quintile were as follows: quintile 1 (060 fg of 5-OHmdU/ng of
dThd), 3 with invasive cancer and 11 with benign lesions;
quintile 2 (6191 fg/ng of dThd), 5 with invasive cancer and 10 with
benign lesions; quintile 3 (92145 fg/ng of dThd), 5 with invasive
cancer, 6 with high-risk lesions, and 3 with benign lesions; quintile 4
(146308 fg/ng of dThd), 4 with invasive cancer, 9 with high-risk
lesions, and 2 with benign lesions; and quintile 5 (>308 fg/ng of
dThd), 6 with invasive cancer, 7 with high-risk lesions, and 2 with
benign lesions.
In 13 women, a second blood sample was obtained at a follow-up
clinic visit, after the results of the biopsy were known. This included
2 women with high-risk biopsies and 11 women with invasive cancer who
had not begun treatment. Average time post biopsy or surgery (if
surgery was also done) was 10.2 days (SD = 5.5 days; range, 321
days). There was no significant difference between the levels of
5-OHmdU pre and post biopsy by the Wilcoxon signed-rank test
(P = 0.414; for samples obtained before biopsy,
mean ± SD, 303 ± 257 fg/ng of dThd; median, 218 fg/ng of
dThd; for samples obtained after biopsy, 248 ± 245 fg/ng of dThd,
mean ± SD; median, 191 fg/ng of dThd). This would suggest that
differential psychological factors associated with the clinic visits
(i.e., anxiety that a biopsy is needed) or any effects of
having had surgery or biopsy in the recent past did not appreciably
affect 5-OHmdU levels.
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Discussion
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Oxidative DNA damage has been suggested previously to be
associated with increased cancer risk (16)
. Levels of such
damage can be envisioned to represent the net result of oxidant
exposures via environmental or endogenous sources and DNA repair
ability. For example, family history of breast cancer in primary
relatives has uniformly been shown to be associated with decreased DNA
repair ability of lymphocytes (3, 4, 5, 6)
.
Some studies, but not all, suggest that levels of oxidative DNA
damage are higher in human breast tumor tissue than in normal breast
tissue (17, 18, 19, 20)
. This is also evident in blood, with
higher levels of oxidative DNA damage having been indicated in breast
cancer cases versus controls (1
, 2)
. In the
study of Frenkel et al. (2)
, blood was obtained
0.56 years before the diagnosis of breast cancer was made, which
helps to implicate oxidative damage in cancer etiology. In that study,
women with self-reported benign breast disease (chiefly fibrocystic
disease) or a family history of breast cancer with no reported breast
problems also exhibited higher serum antibodies to 5-OHmdU
versus controls, which is a measure of 5-OHmdU levels in the
DNA of WBCs (2)
.
There is sparse literature available on the association of
high-risk breast lesions with biomarkers of oxidative stress and cancer
risk. In one study, lymphocytes of eight women with preinvasive lesions
of the breast exhibited decreased repair of X-ray-induced DNA damage
(4)
. In another study, women with dense mammogram
patterns, which are associated with increased breast cancer risk, were
shown to have relatively increased levels of malondialdehyde in their
urine, indicating increased levels of systemic lipid peroxidation
(21)
. These studies are consistent with our
findings of relatively increased oxidative DNA damage levels in blood
of women with high risk breast lesions
The low-risk control women in our study may not be true controls
because a biopsy was performed. There is evidence that a history of
breast biopsy places a woman at increased breast cancer risk
(22)
. Thus, if we had been able to enroll women with clear
mammograms with no reason for biopsy, levels of oxidative DNA damage
may have been even lower. The lesions we categorized as benign,
however, have typically been associated with very low or no risk for
subsequent invasive breast cancer (23)
.
To the best of our knowledge, this is the first report of oxidative DNA
damage levels in blood of women with atypical hyperplasia or carcinoma
in situ, both of which are associated with a substantial
increase in risk of invasive breast cancer (10)
. The
observations that these women have mean levels of 5-OHmdU similar to
those of women with invasive breast cancer indicates that
oxidative DNA damage may play a role in placing these women at
increased risk for breast cancer.
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Footnotes
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 Supported by Cancer Center Support Grant
CA-22453 from the NIH. Presented in part at the 89th Annual Meeting of
the American Association for Cancer Research, New Orleans, LA, 1998. 
2 To whom requests for reprints should be
addressed, at Barbara Ann Karmanos Cancer Institute, Wayne State
University, Detroit, MI 48201. 
3 The abbreviations used are: 5-OHmdU,
5-hydroxymethyl-2'-deoxyuridine; dThd, thymidine. 
Received 7/ 5/00;
revised 11/ 2/00;
accepted 11/14/00.
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