Although lung cancer remains the leading cause of cancer death worldwide, female breast cancer is now the most commonly diagnosed cancer in the world. The reasons behind the increase in breast cancer can be understood from the changes in prosperity and population structure that have been taking place in countries around the world over the past several years. These were explained in the Prism Series episode on Demographic Transition.
The episode included the following figure that shows the changes in population when a poor country transitions to becoming wealthy.
Figure 1
Source : Our World in Data
https://ourworldindata.org/demographic-transition
Poor countries generally have high mortality rates, particularly in children and young people and life expectancy is short. In order to sustain the population, the birth rate is high. As a consequence, the population tends to have relatively few older people in comparison to the young
As the country becomes more prosperous, the causes of the high mortality can be addressed, fewer children and young people die and life expectancy increases. This leads to an increase in the population, which becomes stabilised as the birth rate begins to fall. As a consequence of the changes, older people come to predominate in the population and young people form a smaller proportion.
Implications for cancers of the cervix and breast
Figures 2 and 3 below show the age specific incidence rates for cancers of the cervix and breast.
Figure 2
Source : Cancer Research UK
https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/cervical-cancer/incidence#heading-One
Figure 3
Source : Cancer Research UK
https://www.cancerresearchuk.org/health-professional/cancer-statistics/statistics-by-cancer-type/breast-cancer/incidence-invasive#heading-One
The incidence of cancer of the cervix peaks around the age of 30. In contrast, the incidence of breast cancer increases with increasing age from around the age of 30.
You might expect, therefore, that a predominantly young population will be more affected by cancer of the cervix than breast cancer, whereas a predominantly older population will be more affected by cancer of the breast. And that is broadly what is found. The highest incidence rates of cancer of the cervix are in low and middle income countries, whereas beast cancer is more common in countries with a high Human Development Index.
Deaths from cancers of the breast and cervix
Countries with few resources have difficulty in providing a wide range of health services, which is the opposite of the position in high income countries. So you might expect that death rates in low income countries from both cancers will be high. You might also expect something similar for countries that are transitioning to become higher income countries. What you find is : -
- Around 90% of deaths from cancer of the cervix occur in low and middle income countries.
- Although breast cancer is more common in countries with High Human Development Index, death rates are lower when compared to countries that score low on the Human Development Index
- Death rates from both cancers are higher in transitioning countries compared to transitioned countries.
The impact of HIV on Cancer of the cervix
For cancer of the cervix, low income countries particularly in Africa where HIV rates are high, have the added disadvantage that women with HIV are 6 times more likely to develop cancer of the cervix than the general population. And an estimated 5% of all cervical cancer cases are attributable to HIV. This can be detected from Map 1, where poor sub-Saharan African countries, which also have high rates of HIV, show high rates of cancer of the cervix. In fact, 20% of children who lost their mother to cancer do so due to cancer of the cervix.
Map 1
Source : WHO
Causes
a) Cancer of the cervix
Risk factors/cause : The Human Papilloma Virus (HPV) transmitted by sexual intercourse is responsible for around 95% of cervical cancer. It may take 15 – 20 years for abnormal cells caused by the virus to develop into cancer, though this may be just 5 – 10 years if the immune system is weakened e.g. by HIV. Ways to tackle the problem include
Prevention : There is now a vaccine against the virus and being vaccinated around the age of 9 – 14 years is an effective way to prevent the HPV infection. This is a key long term approach to the problem.
Other ways to prevent HPV infection in the short term include
- Being a non-smoker or stopping smoking
- Using condoms
- Voluntary male circumcision
Early Diagnosis - Screening : Screening women from the age of 30 can detect disease of the cervix and treatment can prevent it from developing into cancer.
Treatment : Quality treatment can cure cervical cancer, provided that it is detected early and treatment is prompt.
b) Cancer of the breast
Risk factors/cause : Older age is the main risk of developing breast cancer, but it is calculated that in the UK, around 23% of cases are preventable, the two main lifestyle risk factors being obesity (8%) and alcohol (8%) with many other factors that can contribute.
Unlike cervical cancer, therefore, there is no vaccine that can be used to prevent the disease. A key to reducing mortality is to achieve early diagnosis followed by surgery and radiotherapy/ chemotherapy before there has been spread to other parts of the body.
Early Diagnosis - Screening : A good quality screening programme and trained workforce of sufficient size is essential to achieve early diagnosis.
Treatment : Surgery can be curative if the condition is identified early. Radiotherapy and chemotherapy are used where there is the slightest hint of spread.
Wealthy countries can afford this, but poor countries cannot. Countries that are transitioning experience an increase in the incidence of breast cancer on account of the change in age structure of the population, but do not yet have the resources or infrastructure to support a screening programme and high quality integrated services. As a consequence, it is only the fully transitioned countries with high incomes where the death rate from breast cancer has fallen. Distant metastatic spread is higher in sub-Saharan Africa, when compared, for example, with North America.
The future
As more countries move through the population transition, more women will develop breast cancer and there will be an increased demand for services. Today’s episode of the Prism Series looks at the challenges faced when developing a breast cancer service. We are grateful to Dick Rainsbury, former breast surgeon at Winchester, for being with us to describe the work in which he has been involved in Zimbabwe.
Resources/References
Global Cancer Statistics 2020: GLOBOCAN Estimates of Incidence and Mortality Worldwide for 36 Cancers in 185 Countries https://acsjournals.onlinelibrary.wiley.com/doi/10.3322/caac.21660
CANCER OF CERVIX
Key Facts from WHO :
https://www.who.int/news-room/fact-sheets/detail/cervical-cancer#:~:text=Cervical%20cancer%20is%20the%20fourth,%2D%20and%20middle%2Dincome%20countries.
Cervical cancer in low and middle-income countries
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7400218/
BREAST CANCER
Key Facts from WHO
https://www.who.int/news-room/fact-sheets/detail/breast-cancer
Global Stage Distribution of Breast Cancer at Diagnosis: A Systematic Review and Meta-Analysis
https://pubmed.ncbi.nlm.nih.gov/37943547/
Breast Cancer in Low- and Middle-Income Countries
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6277976/
Community health workers and early detection of breast cancer in low-income and middle-income countries: a systematic scoping review of the literature
https://gh.bmj.com/content/5/5/e002466#:~:text=The%20incidence%20and%20mortality%20due,those%20who%20live%20in%20LMICs.
