The Relative Risk of breast cancer
The relative risk ratio is a number used to calculate breast cancer risk factors according to specific behaviors or circumstances.
This risk ratio number is multiplied by the normal risk number to calculate a specific risk that comes from having a particular given risk factor.
For example, for women with a family history of breast cancer, or other high risk factors, the relative risk ratio is a means of understanding the proportional increase in the risk of developing breast cancer due to these specific factors.
‘A bit more’ about Relative Risk Factors
So, for example, the cumulative risk of breast cancer for a 40 year old woman is 1 in 68 according to SEER statistics (1975 – 2009). This statistic has been established as a useful baseline for measuring increased breast cancer risk.
For example, if a woman drinks over 30 g of alcohol per day her relative risk factor for breast cancer is about 1.32. That is, this woman is 1.32 times more likely to develop breast cancer compared to women of the same age who do not take alcohol.
Another statistical way of looking at it, is that a relative risk of 2.5 means that for every 68 women of age 40, 2.5 are likely to develop breast cancer in their remaining lifetime, instead of the normal rate of one woman.
Relative Risk as a Percentage
Odds ratio: Another measure of Breast Cancer Risk
Occasionally one finds the term ‘Odds Ratio’ in studies of risk factors for breast carcinoma.
The odds-ratio is a term commonly used in mathematics and probability. The odds ratio compares whether the probability of an event is the same for any two groups.
Specifically, it measures the difference between an experimental group with a particular risk factor and a control group without.
In breast cancer risk ratios, the variables are the risk factors. The relative risk ratio is an odds ratio comparing women who have a certain risk factor as compared to women who do not.
Breast Cancer Risk Factors
We will not go into all of the breast cancer risk factors here as we have two brand new posts on the following, with all the latest information.
New Post 1) Breast Cancer risk factors that you can’t change
- Increasing Age
- Risk of Breast Cancer according to the country that you live
- Family history of breast cancer
- Genetic risks (including BRCA1 and BRCA2)
- Dense breast tissue
- Race and Ethnicity
- Some Benign Breast Cancers
- Ductal Carcinoma in-situ
- Hormones: The age of menarche and menopause
Note: Increasing age is certainly an increased risk factor for developing breast cancer, but it is generally not included in discussions of risk ratios. It is assumed that, all other factors being equal, increasing age poses the same heightened risk of breast cancer for all women.
New Post 2) Breast Cancer Risk Factors that you CAN change
- Alcohol intake, with an increased relative risk according to the more alcohol consumed per day
- Obesity
- Hormone Replacement Therapy (HRT)
- Use of Oral Contraception
- Smoking
More on Breast Cancer Risk Factors
The factors that can increase a woman’s risk of breast cancer is the subject of intensive current research.
However, the most significant factor of increasing breast cancer risk is age. The older a woman is, the higher her risk of breast cancer. Indeed, the age-effect is stronger than any other risk factor for breast cancer.
Other factors (not in included on our 2 new breast cancer posts) now being considered as true breast cancer risk factors include age at first live birth and the number of full term pregnancies.
The relationship between pregnancy and breast cancer is complex. According to one medical study, each pregnancy including the first, increases the risk of early-onset breast cancer immediately after the birth.
However, early age of first pregnancy (under 34) is highly protective against late-onset breast cancer. In fact, the younger a woman is at the age of the first birth, the lower the breast cancer risk.
Subsequent births also reduce the overall risk of breast cancer. Furthermore, breast feeding for ‘long periods’ is also thought to have a protective effect.
Older Information from this post that is still relevant
Traditional pathological risk factors
The table below shows traditional pathological risk factors, increasing relative to an average woman without those factors.
For example, a risk factor or ratio of 2, seen below with the presence of a solitary papilloma is around 2:1. In other words, twice as likely as a woman with no risk factors, of developing breast cancer.
Again, these risk factors are geared towards a woman of 40 years old, which is thought to be an essential time for breast cancer screening. Aged 40 is also around the time when the most women first come in contact with the disease.
‘Screening’ risk factors: hyperplasia, papilloma, history, prior treatments
| Risk Factor | Relative Risk for breast cancer |
| Solitary Papilloma | 1.5 to 2 |
| Proliferating lesions | 1.6 to 2.1 |
| Personal History | 2-3 |
| Family History | 2.5 |
| Atypical Intraductalr hyperplasia (ADH) | 4.4 to 5 |
| ADH associated with positive family history | 8 |
| Thoracic irradiation | 10 |
Breast Cancer risk due to various proliferative lesions
The relative risk for someone who has had proliferative lesions is 1.6 to 2.1.
Proliferative lesions have rapidly growing breast tissue, which may or may not be classified as cancerous or abnormal. For example moderate to florid hyperplasia, or sclerosing adenosis,
A solitary papilloma is a benign epithelial cell tumor and increases the risk by about two times.
Pathological Conditions with NO increased breast cancer risk
There is no evidence for increased risk for breast cancer for women with:-
- Duct ectasia
- Plasma cell mastitis
- Fibroadenoma without degenerative change
- Non proliferative fibrocystic changes, such as mild epithelial hyperplasia (without atypia), fibrosis, cysts, adenosis and apocrine metaplasia
Risk of breast cancer greatly increased with atypical ductal hyperplasia
A substantially increased relative risk of 4.5 to 5 is present with atypical ductal hyperplasia.
‘Atypical’ means that the size and shape of new cells are not developing as anticipated, which could indicate carcinoma.
The relative risk for someone with Atypical Ductal Hyperplasia, and a positive family history of breast cancer is very high, at 8 times that of a non-affected woman.
However, the risk associated with atypical hyperplasia (ADH) actually decreases with age.
Lobular hyperplasia and Lobular carcinoma in situ risk ratios
Lobular hyperplasia indicates that the rapid cells growth is occuring in and around the breast lobules, not the breast ducts.
Wheras lobular carcinoma in situ, means that malignant carcinoma has been verified in the breast lobules, but still at a very early stage.
With Atypical lobular hyperplasia, which implies genetic mutations present in some new cells within the breast lobules, there is a significant increase in the risk of invasive breast cancer, ranging from 4 to 10 times.
However, in lobular carcinoma in situ, the risk of breast cancer is very high, at 8 to 10 times that of a normal, healthy breast.
Ductal carcinoma in situ (DCIS) also presents an increased relative risk of 8 to 10 times. However, lobular neoplasia is not considered as serious as ductal neoplasia.
We have a brand new post on Prognostic Factors and Survival rates for Ductal Carcinoma In-Situ
Relative Risk and therapeutic management options for non invasive breast lesions
Experienced physicians will assess the relative risk associated with screening indicators, such as age, overall health and personal situation to determine the best follow-up plan.
If necessary, theraputic interventions may be advised. Usually, if any of the risk factors associated with increased risk ratios are revealed at cancer screening, annual clinical follow-up is considered mandatory.
However, a lumpectomy or the use of radiation therapy would be unlikely unless a diagnosis of ductal carcinoma in situ is confirmed.
| Lesions | Relative Risk | Clinical Exam | Diagnostic Mammography | Management |
| ductal hyperplasia , without atypia | 1.5-2 | annual | annual for 3 years if core biospy | clinical follow-up |
| atypical ductal hyperplasia | 4-5 | annual | annual | excisional biopsy |
| atypcial ductal hyperplasia with family history | 6-8 | Annual | annual | excisional biopsy |
| Lobular neoplasia, lobular carcinoma in situ | 4-10 | annual | annual | clinical follow-up |
| DCIS | 8-10 | annual | annual | tumorectomy and radiotherapy |
A couple of Questions and Answers
What is the difference between ‘Relative risk’ and ‘Absolute risk’?
Relative risk is the number that tells you how much something you do, such as maintaining a healthy weight, can change your risk. This of course, is in comparison to your breast cancer risk if you are very overweight.
Relative risk can be expressed as a percentage increase. If something you do or take doesn’t change your risk, then the relative risk reduction is 0% (no difference). However, if something you do or take lowers your risk by 30% compared to someone who doesn’t take the same step, then that action reduces your relative risk by 30%. If something you do triples your risk, then your relative risk increases by 300%.
Absolute risk: is the size of your own personal risk. Absolute risk reduction is the number of percentage points your own risk goes down if you do something protective, such as stop drinking alcohol. The size of your absolute risk reduction depends on what your risks are to begin with.
What are some unknown risk factors for breast cancer risk factors?
There are some early, inconclusive medical studies that indicate the following factors may be linked with an increased risk of breast cancer. However, more research is needed for definitive results.
- Diethylstibestrol (DES) A type of artificial estrogen prescribed to pregnant women between 1940 and 1971.
- Diet: A diet low in vegetables and fruit or high in fat, soy, red meat or cadmium
- Thyroid disease
- Anxiety and Stress
- Lack of exercise
- History of melanoma
- Chemicals, such as deodorant
REFERENCES:
- Altekruse SF, Kosary CL, Krapcho M, et al, SEER Cancer Statistics Review, 1975-2007. Bethesda, MD: National Cancer Institute; 2010 (Retrieved 02 April 2017) https://seer.cancer.gov/archive/csr/1975_2007/
- Kobayashi S, Sugiura H, Ando Y, Shiraki N, Yanagi T, Yamashita H, Toyama T. (2012) Reproductive history and breast cancer risk. Breast Cancer. 2012 Oct;19(4):302-8. https://www.ncbi.nlm.nih.gov/pubmed/22711317
Back to Updated Breast cancer Incidence and Mortality list of posts or our new breast cancer website.
