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Lifetime physical activity and its effects on breast cancer survival

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Lifetime physical activity and its effects on breast cancer survival

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LIFETIME PHYSICAL ACTIVITY AND ITS EFFECT ON BREAST CANCER
SURVIVAL

by

Carmen Nicole West-Wright
________________________________________________________________

A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(APPLIED BIOSTATISTICS/EPIDEMIOLOGY)

May 2008

Copyright 2008 Carmen Nicole West-Wright

ii

Acknowledgements
I would like to thank my graduate advisor and committee chair Dr. Leslie
Bernstein for her guidance and encouragement during the process of completing
my thesis. I would also like to thank my committee members Dr. Giske Ursin and
Dr. Dennis Deapen for their support.

iii
Table of Contents
Acknowledgements ii
List of Tables iv
Abstract v

Introduction 1

Chapter 1: Methods 2
Setting 2
Study Participants 2
Measurement of Follow-up 3
Measures of Recreational Physical Activity 3
Assessment of Breast Cancer Risk Factors 5
Statistical Analysis 6

Chapter 2: Results 7

Chapter 3: Discussion 15
Conclusion 17

Bibliography 18

iv
List of Tables

Table 1: Selected baseline characteristics of women diagnosed 8
with breast cancer from 1995-2004 in the California
Teachers Study in relation to cause of death

Table 2: Multivariable relative risk (RR) and 95% confidence interval 10
(CI) for the association between physical activity prior to
diagnosis and death by cause among women diagnosed
from 1995-2004 in the California Teachers (RR stratified by age)

Table 3: Multivariable relative risk (RR) and 95% confidence interval (CI) 12
for the association between physical activity and breast cancer
mortality by estrogen receptor (ER) status among women in the
California Teachers Study

Table 4: Multivariable relative risk (RR) and 95% confidence interval (CI) 14
for the association between physical activity and breast cancer
mortality by stage of disease among women in the California
Teachers Study

v
Abstract

Introduction: Physical activity has long been suggested as a modifiable lifestyle
factor that aids in the reduction of breast cancer risk (1-13). The relationship
between physical activity and breast cancer survival is not as clearly defined as
the association with risk.
Methods: We examined the association of lifetime recreational physical activity
on breast cancer survival in a cohort of 133,479 women established in 1995-
1996 who had a first primary invasive breast cancer after completion of the
baseline questionnaire, 3190 women were included in this analysis.
Results: Summarized lifetime was strongly predictive of the risk of dying from
breast cancer for patients irrespective of estrogen receptor status and was
predictive of all causes of death for patients with ER- breast cancers.
Conclusions: These results suggest that physical activity prior to breast cancer
diagnosis particularly, lifetime physical activity, may decrease the risk associated
with death from breast cancer or from any cause.

Introduction
Risk factors such as, family history of disease, late age at first child birth,
menarche and menopause, that have been established for breast cancer thus far
are not easily altered by interventions. Physical activity has long been suggested
as a modifiable lifestyle factor that aids in the reduction of breast cancer risk (1-
13). Current studies strongly support an inverse relationship between physical
activity and postmenopausal breast cancer but are not as strong for
premenopausal breast cancer (14). The exact mechanism by which physical
activity reduces breast cancer remain unclear but it is known that endogenous
sex hormones are important in the development of breast cancer as observed by
the association with menstrual cycle and reproductive factors such as age at
menarche, first birth and menopause (15-17) and it has been shown that physical
activity has an effect on menstrual characteristics such as later age at menarche
and anovulatory (18) and on body size which affects exposure to estrogen in
postmenopausal women (19-20). Other biological pathways relating to
metabolism, immune functions and lipid peroxidation, provide further support for
the observed protective effect (21-24).
The relationship between physical activity and breast cancer survival is
not as clearly defined as the association with risk. Some studies have shown no
association between physical activity prior to diagnosis and breast cancer
survival (25-26), while others suggest a possible protective effect when
assessing physical activity levels one year prior to diagnosis (27) and physical
activity levels post-diagnosis (28). The importance of timing, duration and

2
intensity of physical activity on breast cancer survival remain mostly unanswered.
In an attempt to address these issues we examined the association of lifetime
recreational physical activity on breast cancer survival in a large cohort of
California teachers.
Methods
Setting
Detailed information on the California Teachers Study has been reported
previously (29). In brief, it is a prospective cohort study of 133,479 female public
school teachers and administrators who were currently working or retired and
members of the California State Teachers Retirement System at the time the
study began in 1995. Members of the cohort completed a detailed questionnaire
that was mailed in 1995.
Study Participants
Women were eligible for the study if they had a first primary invasive breast
cancer after completion of the baseline questionnaire. Incident cases of invasive
breast cancers (International Classification of Disease Oncology topography
codes (ICD9-174, ICD10-C50) were identified through annual linkages of the
California Teachers Study database with the California Cancer Registry. Of all
cancers in California 99% are reported to the California Cancer Registry from
regional registries throughout the state as part of a state mandate. Overall we
had 3190 participants who were living in California when diagnosed with a first
primary invasive breast cancer after joining the cohort but before January 1, 2004

3
who had provided complete information on physical activity and history of
comorbid conditions.
Measurement of Follow-up
Follow-up began on the date of breast cancer diagnosis and continued to death
(n=356), or end of the follow-up period on December 31, 2004. The entire cohort
including all cancer patients is monitored through newsletters mailed annually or
mailing of additional questionnaires, annual linkage with the US Postal Service
National Change of Address database, and change-of-address postcards
submitted by participants. Deaths in the cohort are ascertained through linkages
with the California state mortality files, the Social Security Administration death
master file and the National Death Index. For all deaths, date and cause of
death are recorded. We did not review cause of death and here, utilize the
causes of death recorded on the death certificate.
Measures of Recreational Physical Activity
Detailed information on recreational physical activity was obtained from the
baseline questionnaire. Participants provided information on activities at specific
time periods throughout their lives (during high school, between the ages of 18
and 24, 25 and 34, 35 and 44 and 45 and 54 years). Participants also provided
information on their recreational activities during the 3 years prior to completing
the questionnaire. They were asked to report participation in the following
activities, for each time period: moderate activities (for example brisk walking,
golf, softball, volleyball, recreational tennis, and cycling on flat surfaces) and

4
strenuous activities (running, jogging swimming laps, aerobics, racquetball,
aerobics, calisthenics and cycling on hills). Participants were asked to report the
average number of hours per week (categories: none, 0.5, 1, 1.5, 2, 3, 4-6, 7-10
and >11) and months per year (categories: 1-3, 4-5, 7-9 and 10-12) that they
engaged in moderate and strenuous activities. For each time period we created
separate “hours per week” variables for moderate and strenuous physical activity
by multiplying the hours spent per week by the portion of the year in which the
woman engaged in the activity. The midpoint value of each category range was
used to make this calculation and >11 hours per week was assigned a value of
12. We multiplied the average hours per week per year of activity done during a
specified time period (high school and between the ages of 18-24, 25-34, 35-44,
and 45-54 years) by the number of years the women spent in each relevant time
period and then summed across all of the time periods to calculate her “lifetime”
physical activity. This number was then divided by the total number of years
spent in all the time periods to get an average annual lifetime (high school to <55
years at baseline) or a partial-average (if 55 years of age or older at baseline)
annual lifetime measure of physical activity for each woman. We created all
three physical activity variables; strenuous, moderate and a variable that
combined strenuous with moderate activity. The lifetime strenuous and lifetime
moderate physical activity variables were categorized into four groups (≤0.50,
0.51-1.50, 1.51-3.00, ≥3.01 hrs/wk). The strenuous moderate grouped variable
was classified as low-low (both moderate and strenuous activity variables

5
categorized as < 0.5), any-intermediate activity (either strenuous or moderate
categorized between 0.51 and 3.00 hrs/wk) and any-high (either strenuous or
moderate activity categorized as > 3.01 hrs/wk).
Assessment of Breast Cancer Risk Factors
The baseline questionnaire provided information on factors that were considered
pertinent for breast cancer risk including race and ethnicity, personal and family
history of breast cancer, lifestyle factors (recreational physical activity and diet),
weight and height, history of comorbid diseases and hormone therapy use (29).
Data on estrogen receptor and progesterone receptor status and stage of
disease at the time of diagnosis were obtained from California Cancer Registry
records.
Body mass index (BMI, weight at baseline in kg divided by the squared
value of height at baseline in meters) was categorized into four groups: <25, 25-
29.99, ≥30 kg/m
2
or unknown. Total caloric intake at baseline was assessed
using the 1995 validated version of the Block food-frequency questionnaire (30).
At baseline, we collected information on the presence or absence of a personal
history of diabetes, high blood pressure, heart attack/myocardial infarction or
stroke. We created a summary comorbidity variable which is a count of the
number of these comorbid conditions that a woman reported and categorized this
variable into three groups: 0, 1 or 2+. Stage of disease was defined by two
categories: local (n=2185) or non-local, which includes regional (n=920),
metastatic (n=59) and unknown stage (n=26).

6

Statistical Analysis
Cox proportional hazards regression models were used to calculate the relative
risk (RR) of death from breast cancer or from death from any cause associated
with a woman’s physical activity prior to diagnosis. Hazard rate ratios, presented
as relative risk with 95% confidence intervals (95% CI) were estimated using age
in days at the start and end of follow-up as the time variable. In the primary
analysis death from breast cancer was the end point and death from any other
cause was censored. In a secondary analysis all causes of death were the
endpoint of interest.
Multivariable models were used to evaluate the associations between
physical activity level prior to diagnosis and breast cancer survival. Models were
stratified by age at baseline in years and adjusted for race (White versus Non-
White), BMI, total caloric intake, history of comorbid diseases and tumor receptor
status and stage of breast cancer at diagnosis. The RR’s are presented for each
category of physical activity in hours per week. The less than 0.50 hours per
week was the reference group. We conducted a trend test for the relative risk of
each physical activity category by fitting the median value for each activity level
as a continuous variable in the age-stratified, multivariable-adjusted models. We
examined the effect of physical activity on breast cancer survival according to
stage and estrogen receptor status. In our models, we first fit each of the
comorbid conditions individually and then fit the 3 category variable of the count

7
of comorbid conditions. As these two approaches fit the data equally well, we
present results for the models adjusting for the summary count variable. Further
we initially adjusted for receptor status using a five category variable, ER-PR
positive, ER-positive/PR-negative, ER-negative/PR-positive, ER-PR negative and
one or both receptor statuses unknown. As the results for the more extensively
adjusted model were similar to those for a model that adjusted only for estrogen
receptor status, we present results for this simplified model. Kaplan-Meier
survival curves plotted for each activity group were used to check the
proportional hazards assumptions; no violations were observed. P=.05 was
considered statistically significant, two-sided Ps are reported for tests for trend.
All analyses were performed using SAS version 9.1
Results
Table 1 presents the baseline disease characteristics of the 3190 women
diagnosed with invasive breast cancer in our cohort. The mean age at diagnosis
was 59.1 and women ranged from 26-94 years. The majority of women, 90.3%,
were white. Among women with known BMI, over half, 55.2%, of the women had
a body mass index (BMI) less than 25 kg/m
2
at baseline, with very few, 12.9%,
being obese. The majority, 71.2%, of women with estrogen receptor status
available in the medical records had estrogen receptor positive (ER+) tumors.
But when we observe deaths, the ER+ tumors account only for 53.0% of the
breast cancer deaths and 63.2% of the deaths due to all causes.

8
Table 1: Selected baseline disease characteristics of women diagnosed with
breast cancer from 1995-2004 in the California Teachers Study in relation to
cause of death
Total
(N=3190)
Breast Cancer
Deaths
(N=183)
All Causes of
Death*
(N=356)

Age
Mean (SD)
Range

59.11(11.79)
26-94

Race
White
Non-White

2879
311

166
17

322
34

Body Mass Index (kg/m
2
)
< 25
25-29
30+
Missing/unknown

1762
877
413
138

83
49
35
16

176
89
58
33
Total Caloric Intake (kcal)
<1271
1271-1682
> 1682
Missing/unknown

957
955
986
292

62
44
52
25

116
99
82
59
Estrogen Receptor Status
Positive (+)
Negative (-)
Missing/Unknown/borderline

History of Disease
¥

0
1
2+

2270
409
511

2396
691
103

97
53
33

131
40
12

225
72
59

211
114
31
Disease Stage
£

Local
Non-local

2185
1005

51
132

181
175

Note: * Includes breast cancer and other causes of death: cancers other than breast cancer (49), cardiovascular disease
(52), cerebrovascular disease (21), thrombosis (3), cardiopulmonary and pulmonary diseases (20), diabetes (3), other
(24) and external cause (1).
¥
Includes personal history of stroke, heart attack, diabetes and high blood pressure.
£
Non-
local includes regional and metastatic disease.

9
Twenty-four percent of the women reported at least one comorbid
conditions. A total of 99 women reported diabetes, 711 reported high blood
pressure, 50 a heart attack and 45 a stroke at baseline. However among those
who died from any cause, 60% had a history of at least one of these comorbid
conditions. The majority of breast cancer patients (68.5%) were diagnosed with
localized disease, but the majority of breast cancer deaths (72.1%) occurred
among women with more advanced disease,.
Risk of breast cancer death decreased with increasing level of lifetime
strenuous exercise activity, however, the trend in risk was not statistically
significant (Table 2). Women whose lifetime average strenuous activity was
more than 3 hrs/wk were 32% less likely to die from breast cancer than those
whose average was no more than 0.5 hrs/wk (RR=0.58, 95% CI=0.41-1.14).
Lifetime strenuous activity was not associated with risk of dying overall (all
causes of death). Lifetime moderate activity was not associated with risk of
dying from breast cancer, but the trend in risk for all causes of death was of
borderline statistically significance (p-trend=0.06). Evaluating the impact of both
strenuous and moderate activity on risk, women who participated in some
intermediate level activity had 42% lower risk of breast cancer death (RR=0.58,
95% CI=0.39-0.86) and those with high levels of both moderate and strenuous
activity had 50% reduced risk (RR=0.50; 95% CI=0.32-0.78) compared to the
inactive women.

10

Table 2: Multivariable relative risk (RR) and 95% confidence interval (CI) for the
association between physical activity prior to breast cancer diagnosis and death
by cause among women diagnosed from 1995-2004 in the California Teachers

Physical Activity Groups Breast Cancer Deaths All Causes of Death
# Breast
Cancers
Case
s (n)
RR (95% CI)
(RR stratified on
age)
Cases
(n)
RR (95% CI)
(RR stratified on
age)
Lifetime Physical Activity
Strenuous
£

0-0.50 1193 81 1.00 164 1.00
0.51-1.50 750 45 0.95 (0.64-1.42) 90 1.19 (0.90-1.58)
1.51-3.00 630 31 0.88 (0.56-1.41) 48 0.85 (0.60-1.21)
≥ 3.01 617 26 0.68 (0.41-1.14) 54 1.00 (0.70-1.43)
P trend* 0.16 0.69
Moderate
£

0-0.50 733 61 1.00 115 1.00
0.51-1.50 834 47 0.78 (0.51-1.19) 103 1.04 (0.78-1.39)
1.51-3.00 799 38 0.70 (0.45-1.09) 70 0.77 (0.55-1.07)
≥ 3.01 824 37 0.80 (0.50-1.29) 68 0.77 (0.54-1.09)
P trend* 0.40 0.06
Strenuous-Moderate
Grouped Variable
¥

Low-Low 489 46 1.00 85 1.00
Any-Intermediate 1613 91 0.58 (0.39-0.86) 180 0.84 (0.63-1.11)
Any-High 1088 46 0.50 (0.32-0.78) 91 0.70 (0.51-0.96)
Past 3 Years Physical
Activity

Strenuous
£

0-0.50 1995 128 1.00 256 1.00
0.51-1.50 445 19 0.74 (0.44-1.25) 39 0.84 (0.58-1.20)
1.51-3.00 378 19 0.85 (0.50-1.47) 33 0.93 (0.62-1.38)
≥ 3.01 372 17 0.78 (0.45-1.36) 28 0.81 (0.53-1.24)
P trend* 0.36 0.29
Moderate
£

0-0.50 1052 64 1.00 153 1.00
0.51-1.50 693 41 1.45 (0.94-2.24) 75 1.01 (0.75-1.38)
1.51-3.00 726 39 1.25 (0.80-1.95) 67 0.86 (0.62-1.18)
≥ 3.01 719 39 1.24 (0.79-1.95) 61 0.77 (0.55-1.07)
P trend* 0.53 0.09
Strenuous-Moderate
Grouped Variable
¥

Low-Low 879 56 1.00 132 1.00
Any-Intermediate 1428 82 1.26 (0.87-1.84) 151 0.93 (0.72-1.20)
Any-High 883 45 1.06 (0.69-1.65) 73 0.73 (0.54-1.00)

11
For all causes of death, the impact not as strong, with those in the highest
category of lifetime activity at 30% lower risk of death compared to the least
active women (RR=0.30, 95% CI=0.51-0.96).
Recent activity prior to diagnosis, activity in the 3 years before entering the
cohort, was not strongly related to the risk of breast cancer death. For all causes
of death, increasing level of recent moderate activity was modestly associated
with decreasing risk of death (p-trend=0.09) as was activity among those who
were in the high category of both moderate and strenuous activity relative to
inactive women (RR=0.73, 95% CI=0.54-1.00).
The numbers of ER+ breast cancer deaths (n=97) and ER- breast cancer
deaths (n=53) are small. Lifetime activity summarized as low, any intermediate
or high was strongly predictive of the risk of dying from breast cancer for patients
irrespective of estrogen receptor status and was predictive of all causes of death
for patients with ER- breast cancers (Table 3). Strenuous activity in the 3 years
before the joining the cohort was associated with all causes of death for ER-
tumors (p-trend=0.04). Women with ER+ tumors who participated in moderate
physical activity had a borderline statistically significant trend (p-trend=0.07) for
all cause of death. No other associations were observed for recent activity by
receptor status.

12
Table 3: Multivariable relative Risk (RR) and 95% confidence interval (CI) for the
association between physical activity and breast cancer mortality by estrogen
receptor (ER) status among women in the California Teachers Study

Breast Cancer Deaths All Causes of Death
Physical Activity
(h/wk/y)
ER Positive
RR (95% CI)
ER Negative
RR (95% CI)
ER Positive
RR (95% CI)
ER Negative
RR (95% CI)
Lifetime Physical
Activity

Strenuous
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 1.09 (0.64-1.85) 0.69 (0.28-1.72) 1.40 (0.90-2.00) 0.78 (0.37-1.62)
1.51-3.00 0.52 (0.25-1.10) 0.94 (0.36-2.40) 0.73 (0.45-1.20) 0.84 (0.36-1.94)
≥ 3.01 0.81 (0.39-1.67) 0.34 (0.10-1.72) 1.40 (0.90-2.19) 0.40 (0.14-1.17)
P trend* 0.31 0.21 0.35 0.15
Moderate
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 0.83 (0.46-1.49) 0.33 (0.13-0.87) 1.09 (0.75-1.59) 0.56 (0.27-1.18)
1.51-3.00 0.89 (0.49-1.62) 0.66 (0.24-1.79) 0.83 (0.55-1.26) 0.59 (0.24-1.45)
≥ 3.01 0.56 (0.27-1.15) 0.82 (0.31-2.17) 0.67 (0.42-1.06) 0.68 (0.29-1.61)
P trend* 0.12 0.62 0.03 0.59
Strenuous-
Moderate Grouped
Variable

Low-Low 1.00 1.00 1.00 1.00
Any-Intermediate 0.54 (0.32-0.91) 0.30 (0.12-0.75) 0.85 (0.59-1.22) 0.44 (0.21-0.91)
Any-High 0.41 (0.22-0.76) 0.31 (0.11-0.88) 0.78 (0.52-1.17) 0.32 (0.13-0.78)
Past 3 Years
Physical Activity

Strenuous
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 0.69 (0.33-1.47) 0.87 (0.30-2.56) 0.83 (0.51-1.36) 0.57 (0.20-1.64)
1.51-3.00 0.79 (0.36-1.74) 0.71 (0.22-2.25) 0.99 (0.60-1.64) 0.63 (0.21-1.84)
≥ 3.01 1.03 (0.50-2.13) 0.30 (0.06-1.64) 1.12 (0.68-1.86) 0.21 (0.04-1.11)
P trend* 0.84 0.13 0.79 0.04
Moderate
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 1.64 (0.90-3.00) 0.62 (0.22-1.78) 1.09 (0.73-1.61) 0.61 (0.24-1.54)
1.51-3.00 0.95 (0.50-1.80) 1.05 (0.43-2.55) 0.74 (0.49-1.12) 1.01 (0.45-2.29)
≥ 3.01 1.21 (0.64-2.32) 1.37 (0.53-3.54) 0.71 (0.46-1.09) 1.02 (0.44-2.36)
P trend* 0.85 0.39 0.07 0.90
Strenuous-
Moderate Grouped
Variable
¥

Low-Low 1.00 1.00 1.00 1.00
Any-Intermediate 1.14 (0.67-1.93) 0.83 (0.37-1.82) 0.94 (0.68-1.31) 0.67 (0.34-1.34)
Any-High 1.16 (0.63-2.12) 1.00 (0.40-2.53) 0.82 (0.56-1.21) 0.63 (0.28-1.38)

13
Our summary variable that compares intermediate levels and high levels of
moderate and strenuous activity was predictive of the risk of breast cancer death
for women with localized disease, was less strongly associated with risk of breast
cancer death among women with more advanced disease (Table 4). Neither
strenuous activity alone nor moderate activity was associate with risk of breast
cancer death or death from any cause. Activity in the three years prior to
baseline was not associated with risk of dying of breast cancer or dying from any
cancer among women with localized disease or among women with more
advanced disease, although high levels of both moderate and strenuous activity
in the last 3 years appears to be associated with risk of any cause of death
among women with localized disease (RR for high vs. low activity=0.55, 95%
CI=0.43-1.02).

14
Table 4: Multivariable relative risk (RR) and 95% confidence interval (CI) for the
association between physical activity and breast cancer mortality by stage of
disease among women in the California Teachers Study

Breast Cancer Deaths All Causes of Death
Physical Activity
(h/wk/y)
Local
RR (95% CI)
Advanced
RR (95% CI)
Local
RR (95% CI)
Advanced
RR (95% CI)
Lifetime Physical
Activity

Strenuous
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 0.93 (0.41-2.13) 0.95 (0.59-1.54) 1.06 (0.70-1.62) 1.21 (0.81-1.83)
1.51-3.00 0.84 (0.36-2.00) 0.91 (0.51-1.61) 0.77 (0.45-1.32) 1.02 (0.61-1.68)
≥ 3.01 0.50 (0.17-1.45) 0.94 (0.51-1.73) 1.25 (0.76-2.05) 0.94 (0.54-1.65)
P trend* 0.19 0.81 0.67 0.77
Moderate
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 0.67 (0.30-1.50) 0.89 (0.52-1.49) 1.22 (0.80-1.86) 1.02 (0.65-1.59)
1.51-3.00 0.30 (0.11-0.86) 0.80 (0.47-1.37) 0.65 (0.39-1.09) 0.80 (0.50-1.27)
≥ 3.01 0.68 (0.29-1.60) 0.75 (0.41-1.37) 0.77 (0.47-1.26) 0.75 (0.44-1.29)
P trend* 0.48 0.32 0.12 0.22
Strenuous-Moderate
Grouped Variable
¥

Low-Low 1.00 1.00 1.00 1.00
Any-Intermediate 0.37 (0.18-0.78) 0.72 (0.44-1.16) 0.83 (0.56-1.24) 0.89 (0.58-1.34)
Any-High 0.34 (0.15-0.77) 0.60 (0.34-1.03) 0.78 (0.50-1.22) 0.67 (0.40-1.10)
Past 3 Years
Physical Activity

Strenuous
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 0.42 (0.12-1.43) 0.99 (0.53-1.84) 0.77 (0.45-1.32) 1.01 (0.59-1.73)
1.51-3.00 0.71 (0.24-2.12) 1.09 (0.56-2.12) 0.85 (0.47-1.57) 1.25 (0.71-2.22)
≥ 3.01 0.57 (0.18-1.77) 0.97 (0.49-1.93) 0.82 (0.45-1.51) 0.94 (0.49-1.77)
P trend* 0.28 0.90 0.43 0.85
Moderate
£

0-0.50 1.00 1.00 1.00 1.00
0.51-1.50 1.87 (0.78-4.50) 1.32 (0.77-2.26) 1.02 (0.66-1.59) 1.03 (0.64-1.64)
1.51-3.00 1.51 (0.59-3.85) 1.16 (0.69-1.98) 0.92 (0.57-
1.46)
0.89 (0.56-1.41)
≥ 3.01 1.48 (0.623.49) 1.02 (0.58-1.79) 0.71 (0.44-1.14) 0.77 (0.47-1.26)
P trend* 0.61 0.89 0.14 0.22
Strenuous-Moderate
Grouped Variable
¥

Low-Low 1.00 1.00 1.00 1.00
Any-Intermediate 1.25 (0.59-2.64) 1.40 (0.89-2.20) 0.91 (0.63-1.31) 1.15 (0.78-1.70)
Any-High 0.93 (0.41-2.10) 1.09 (0.64-1.85) 0.66 (0.43-1.02) 0.85 (0.53-1.35)

15

Discussion
Previous findings suggest that there is no association between lifetime physical
activity and breast cancer survival (25-26). However, a recent study suggests
that there is a beneficial effect associated with physical activity level one year
prior to diagnosis and breast cancer survival (27). To our knowledge, our study
is the only prospective cohort study to date to report on accumulated long-term
physical activity and breast cancer survival.
An interesting finding in this study is the statistically significant association
between the strenuous/moderate grouped lifetime physical activity variable and
breast cancer survival that does not hold up when we look at strenuous and
moderate alone leading us to believe the use of the summary variable is ideal
because it allows for a cleaner baseline group, all women in the low-low group
were low on both moderate and strenuous physical activity levels.
The past three years physical activity and its effect on breast cancer mortality
do not show any significant protective effects from the physical activity. Evidence
suggests that women’s activity level drops within the first year post-diagnosis
however within three years their level is back up to their pre-diagnosed levels
(31-32). A possible explanation for why lifetime physical activity levels may be
more predictive of better prognosis than past three years could be if women with
lifetime physical activity are the one’s most likely to maintain their activity level
after being diagnosed with breast cancer. If this is the case our lifetime physical

16
activity variables would be a good predictor of physical activity post diagnosis
making our results compatible with previous studies that suggest physical activity
post breast cancer diagnosis increases survival (28).
The combination of lifetime activity level and duration leads to a strong
protective effect in ER+ tumors ranging from 46% to 59% when looking at risk
associated with dying from breast cancer, it does not hold up for risk associated
with dying from any cause. However the finding is even more protective for ER-
tumors decreasing the risk of dying from breast cancer and all causes by up to
70%. Not only does physical activity reduce the risk of ER- breast tumors in this
cohort of California teachers as previously reported (3) it also reduces the risk of
dying from breast cancer or all cause in women with ER- tumors.
Our results also suggest that stage of disease may have an impact on
breast cancer survival. Significantly reduced risk effects were observed for local
stage of disease. A reduced effect was observed for advanced stage but it was
not significant. Despite the small numbers of deaths in local disease we see a
marked effect of physical activity on breast cancer survival however the effect is
not as strong when we look at all causes of death.
Our study has numerous strengths which include its prospective study design,
the ability to identify and confirm cancer diagnosis through the California cancer
registry and detailed data collection on physical activity over multiple age periods
allowing us to assess cumulative lifetime exposure as well as past three years.

17
A couple of potential limitations to our study are the small number of breast
cancer deaths which may have effected our ability to detect potential risk
reductions due to lack of statistical power and our lack of data on other potential
forms of physical activity other than recreational, such as household or
occupational. However we do not expect occupational activity level to vary that
much being that this is a cohort based on a similar occupation.
In summary our results suggest that physical activity prior to breast cancer
diagnosis particularly, lifetime physical activity, may decrease the risk associated
with death from breast cancer or from any cause. The benefit is strongest in
women with ER- tumors and in women with local stage of disease.

18
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Abstract (if available)

Abstract Introduction: Physical activity has long been suggested as a modifiable lifestyle factor that aids in the reduction of breast cancer risk (1-13). The relationship between physical activity and breast cancer survival is not as clearly defined as the association with risk.

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Asset Metadata

Creator West-Wright, Carmen Nicole (author)

Core Title Lifetime physical activity and its effects on breast cancer survival

School Keck School of Medicine

Degree Master of Science

Degree Program Epidemiology

Publication Date 04/14/2008

Defense Date 04/01/2008

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag breast cancer,OAI-PMH Harvest,physical activity

Language English

Advisor Bernstein, Leslie (committee chair), Deapen, Dennis (committee member), Ursin, Giske (committee member)

Creator Email carmenwe@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m1107

Unique identifier UC1281319

Identifier etd-WestWright-20080414 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-51282 (legacy record id),usctheses-m1107 (legacy record id)

Legacy Identifier etd-WestWright-20080414.pdf

Dmrecord 51282

Document Type Thesis

Rights West-Wright, Carmen Nicole

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu