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Descriptive Epidemiology Project
Breast Cancer Prevalence
Maria Jorgensen
Concordia University
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Define the Problem:
Breast cancer is the most prevalent cancer for women in both the developed and
developing world. Breast cancer is the leading cause of cancer deaths of women in the US with
nearly 40,000 women dying annually (Center for Disease Control and Prevention, 2012). The
incidence of breast cancer is increasing due to increased life expectancy, increasing prevalence
of westernized lifestyle and urbanization. Due to the nature of the disease, risk of breast cancer
cannot be reduced significantly by prevention efforts but early screening, detection and treatment
can lead to a more promising prognosis for the patient.
Describe the Agent and Condition:
Breast cancer begins in the breast tissue with cells that are changing and growing out of
control. These cells eventually form a mass referred to as a tumor. The rapid creation of cells and
their abnormalities spread beyond their original boarders and move to other tissue groups in the
body. This process is called metastasis. Breast cancer tumors originate in the glands or the ducts
of the breast tissue.
Tumors are defined by severity levels including: benign, in situ, invasive or infiltrating.
Many tumors are benign and therefore do not cause uncontrollable cell growth and are not life
threatening. In situ breast cancers are split into two categories based on location: in situ within
the ducts (ductal carcinoma in situ, DCIS) or the lobules (lobular carcinoma in situ, LCIS)
(American Cancer Society, 2013). "The majority of in situ breast cancers are DCIS, which
accounted for about 83% of in situ cases diagnosed during 2004-2008"(American Cancer Society,
2013). Many oncology specialists do not consider DCIS or LCIS cancers but rather an indicator
to the patient that they may be at higher risk for further complications with breast cancer.
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Most breast cancers are invasive. Invasive breast cancers start in one area of the breast
and then spread to other breast tissue. Invasive breast cancer is split according to severity at the
initial diagnosis. "The TNM classification of tumors uses information on tumor size and how far
it has spread within the breast and nearby organs (T), lymph node involvement (N), and the
presence or absence of distant metastases (M). Once the T.N. and M are determined, a stage of 0,
1, II, III, or IV is assigned" (American Cancer Society, 2013). Stage 1 is the earliest stage of
cancer, in situ, and stage IV is the most advanced.
Morbidity and Mortality
Breast cancer is a large threat to the health and wellness of women nationally and
worldwide. Breast cancer is the most commonly diagnosed cancer in women and the second
leading cause of death among women in the US. One in every eight women in the United States
will be diagnosed with breast cancer in their lifetime resulting in an estimated 220,000 new cases
diagnosed annually in the United States. Every year 40,000 women die from breast cancer. In the
Estimated Incidence and Mortality Prevalence Worldwide in 2012 table (Figure 1 below), the
percentage of cases resulting in deaths range from 20-45%. The table indicates that those in less
developed regions have a higher likelihood after of mortality after breast cancer diagnosis than
those in more developed regions.
Figure 1: Breast Cancer Estimated Incidence, Mortality and Prevalence Worldwide in 2012
Source: (International Agency for Research on Cancer, 2014)
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Host Characteristics and Risk Factors Associated with Breast Cancer
A woman living in the US has a 12.3%, or a 1 in 8 lifetime risk of being diagnosed with
breast cancer. In the 1970s, the lifetime risk of being diagnosed with breast cancer was 1 in 11
(Center for Disease Control and Prevention, 2012). Increasing rates of diagnosis can be
attributed to longer life expectancy, hormone use by women of menopausal age, increased
prevalence of obesity, and increased rates of breast cancer screenings.
Many risk factors for breast cancer are not modifiable. Today the biggest risk factor for
breast cancer is being female. Males are low risk for breast cancer and make up only 1% of
diagnoses. Age also plays a large role in risk for breast cancer. With increasing age, breast
cancer risk, incidence and death rates increase.
Figure 2: Age- specific Female Breast Cancer Incidence and Mortality Rates, US, 2006-2010
Source: (American Cancer Society, 2013)
Figure 2 above, indicates that towards the ages of 50 to 65 the curve increases rapidly indicating
a high incidence of cases in that population. With people living longer the number of cases in
this age range and above will also increase with life expectancy. "Seventy-nine percent of new
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case and 88% of breast cancer deaths occurred in women 50 years of age and older"(American
Cancer Society, 2013).
Figure 3: Estimated New Female Breast Cancer Cases and Deaths by Age, US, 2013
Source: (American Cancer Society, 2013)
As indicated in Figure 3 above, both in situ and invasive cases of breast cancer experience a ten
fold increase in incidence from the age group <40 to the 50-64 age range.
"Familial history is also a large risk factor for breast cancer. Women with other
incidences of breast cancer within their family can cause an increase of risk by a factor of 2 or 3.
The rare genetic mutations in the BRCA1, BRCA2 and p53 result in high risk for breast cancer
but account for a smaller portion of the total number of breast cancers diagnosed each year.
Risks associated with reproduction hormones present large risk factor increases for individuals
including: having "early menarche (< 12 years old), late menopause, late age at first childbirth,
oral contraceptive use, and hormone replacement therapy"(World Health Organization, 2014).
Breast cancer incidence rates are higher in non-Hispanic white women than African American
women; however, African American women are 40% more likely to die from breast cancer
(Center for Disease Control and Prevention, 2012).
Modifiable risk factors for breast cancer account for 21% of breast cancer deaths. Some
modifiable risk factors include alcohol use, overweight and obesity, and physical inactivity.
Alcohol consumption of greater than 2 drinks per day increases risk for breast cancer by 21%
(American Cancer Society, 2013). The increased risk is dose dependent with more drinks per
day/week increasing risk for breast cancer. This correlation is likely due to the impact of alcohol
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on estrogen and androgen levels. Breast cancer rates have increased with the increased issue of
overweight and obesity in westernized countries. Physical inactivity and obesity have shown
correlations with breast cancer diagnosis. Physical activity before, during and after diagnosis of
breast cancer has shown increased survival rates. At this point, there are no sure preventative
measures against breast cancer, except participating in physical activity and avoiding weight gain.
Obesity increases risk for breast cancer because, in post menopausal women, estrogen is stored
in fat tissue (Komninou, Stephenson, 2004). Being obese creates more fat tissue and therefore
more exposure to estrogen. Higher levels of estrogen exposure are linked to developing breast
cancer. No clear link has been associated between nutrition and breast cancer prevalence.
Environmental attributes
Recently, concerns have been brought up regarding environmental pollutants increasing
cancer rates in the second half of the 20th century from pesticides, industrial chemicals and other
chemicals in the air, drinking water, and consumer products. "In general, epidemiological studies
have not found clear relationships between environmental pollutants and breast cancer, but these
studies have had limited capability to study effects on subgroups of the population or to quantify
exposures at potentially critical periods of life. Furthermore, an association between
environmental exposures and breast cancer may be difficult to quantify because it may reflect an
indirect pathway" (American Cancer Society, 2013)
Social and Economic Factors
Socioeconomic status does not play a large role in getting breast cancer but rather the
stage the disease is diagnosed and treated at. The quality of treatment and speed at which the
individual seeks out treatment is also impacted by socioeconomic status (Ruoran, Rhian, Bernard,
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2013). Those who obtain preventative screenings are more likely to catch tumors in earlier
stages and seek immediate treatment for any precancerous or cancerous cell formations have
higher survival rates. Socioeconomic inequalities appear in late presentation for screening at a
later stage of cancer along with inadequate treatment or access/speed of treatment and play a
large role in the survival rate for this group. (Ruoran, Rhian, Bernard, 2013).
Worldwide, breast cancer ranks in the top ten for cause of death for women in middle and
high income countries which can be attributed to higher life expectancy in these countries (See
Figure 4). Breast cancer is an issue in low income countries as well but the preventative,
diagnostic and treatment care access is much more limited. Women's health in lower income
countries is not considered a high priority due to the allocation of money and low societal status.
"Poverty, less education and a lack of health insurance are also associated with lower breast
cancer survival" (American Cancer Society, 2013).
Figure 4: Ten Leading Causes of Death in Females by Country Income Group, 2004
Source: (World Health Organization, 2009)
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Patterns of mortality during the reproductive years differ greatly between low and high
income countries. In the latter, the three leading causes of female deaths are car accidents,
suicide and breast cancer. In contrast, in low income countries HIV/AIDS, maternal conditions
and tuberculosis account for the three leading causes of death and one in every two deaths
(World Health Organization, 2009). Incidence of breast cancer is higher in high income countries
than in low and middle income countries but mortality rates are similar (See Figure 5). This is
due to access to early detection screenings and also treatments in higher income countries. Early
detection and effective treatment upon diagnosis is essential for survival. Unfortunately, due to
access and affordability, many women in low and middle income countries do not receive
adequate treatment (World Health Organization, 2009).
Figure 5: Incidence and mortality rates of breast cancer and cervical cancer by country
income group (age-standardized per 100,000 women, all ages), 2004
Source: (World Health Organization, 2009)
Temporal variation
Since 1975, the 5 year relative survival rate for both African American and white women
has increased significantly with the current survival rate for white women is 92% and African
American women is 79%. This difference in survival rate can be attributed to stage of cancer at
time of diagnosis and speed and access to treatment. From 1990 to 2010 the death rates
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decreased by 34% as seen in the figure below. The decline is more significant for women <50
with 3.1% decrease per year than women >50 with 1.9% per year. This can be attributed to
improvements in breast cancer screening, detection and treatment (American Cancer Society,
2013).
Worldwide, cases and mortality represent staggering gaps in treatment and detection as
seen in the figure below. Although mortality rates stay in the same range worldwide, the
incidence rate is vastly different. Diagnoses of cancer cases in more developed regions are much
higher than those in less developed regions. Those diagnosed in the less developed regions are
facing a 50% mortality rate in comparison to the 12-20% of more developed areas.
Figure 6: Incidence and Mortality: Estimated age standardized rates (world) per 100,000
Source: (International Agency for Research on Cancer, 2014)
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This distribution of incidence and mortality rates show the need for distribution of
services to areas experiencing high death tolls from breast cancer. Creating preventative
screening clinics to catch cancers in earlier stages could be a helpful preventative measure.
Public health education teaching healthy lifestyle habits recommending diet and exercise,
remaining at a health body weight, abstaining from alcohol, and how to do self breast exams are
all simple measures that could decrease the mortality rates in these less developed regions.
Areas for Improvement in Epidemiology
More research needs to be done for environmental risks such as chemicals in water, air
and consumer products. There is still a debate whether a correlation exists between the increased
pollution of the second half of the century and the cancers occurring in our populations. Also,
creating more cost efficient treatment and screening options so that access to facilities and
effective supplies are more widespread.
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References
American Cancer Society. Breast Cancer: Facts and Figures 2013-2014. Atlanta: American
Cancer Society, Inc. 2013. Retrieved from.
http://www.cancer.org/acs/groups/content/@research/documents/document/acspc042725.pdf
Center for Disease Control and Prevention. (2012). Breast Cancer: Black Women Have Higher
Death Rates from Breast Cancer Than Other Women. CDC Vital Signs.
Retrieved from http://www.cdc.gov/vitalsigns/pdf/2012-11-vitalsigns.pdf
International Agency for Research on Cancer. (2014). Globocan 2012: Estimated Cancer
Incidence Mortality and Prevalence Worldwide in 2012. World Health Organization.
Retrieved from http://globocan.iarc.fr/Pages/fact_sheets_cancer.aspx
Rose DP, Komninou D, Stephenson GD (2004). Obesity, adipocytokines, and insulin resistance
in breast cancer. Obes Rev. 2004. Aug; 5(3):153-65. Retrieved from
http://www.ncbi.nlm.nih.gov/pubmed/15245384
Ruoran Li, MPhil, Rhian, Daniel PhD, Bernard Rachet MD. (2013). How much of
socioeconomic differences in survival in patients with breast cancer can be explained by
differences in stage of diagnosis and treatment? Application of causal mediation analysis
to routine data. The Lancet. 382, 2013. Nov. 561.
doi:10.1016/S0140-6736(13)62486-1
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World Health Organization. (2009). Women and Health: Today's Evidence Tomorrow's Agenda.
(pp. 1-81). Retrieved From
http://whqlibdoc.who.int/publications/2009/9789241563857_eng.pdf
World Health Organization. (2014). Cancer: Breast cancer prevention and control.
Retrieved from http://www.who.int/cancer/detection/breastcancer/en/index2.html