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A recent research has found that some of the genes responsible for determining the cup size of a woman have earlier been found to be associated with breast cancer. So is it right to infer that the size of your breasts determine your risk of breast cancer?
In a breakthrough study, researchers from a California based personal genomics company “23 and Me”, led by Dr. Nicholas Eriksson, have found a possible link between the breast size and the risk of developing breast cancer. Studies, done earlier, have established an association between breast density and breast cancer. Studies have also shown a link between fat deposition on the body and breast cancer. But this is for the first time that a study has shown that the genes involved in breast size and those involved in development of breast cancer may be common.

The study which was published in the 30th June issue of the journal BMC Medical Genetics was conducted on 16,175 of European ancestry. The investigators were trying to find out the genetic factors underlying the breast size of a woman. In order to achieve this, the researchers conducted a genome wide association study (GWAS) in which the women self-reported their bra cup size. Confounding factors like the age of the participants, their genetic ancestry, and history of pregnancies or breast surgeries were taken care of.

The researchers were looking for single nucleotide polymorphisms (SNPs) which are responsible for certain traits, like the breast size, apart from illnesses like cancer, diabetes, and heart disease, etc. SNPs are variations in the normal DNA wherein a single nucleotide in a genomic sequence is altered. They were able to identify seven SNPs associated with the breast size.

What surprised the researchers was the fact that two of these SNPs are also seen in cases of breast cancer. The same allele was found to be associated with increase in breast size as well as increase in the risk of developing breast cancer. Another SNP associated with breast size was found in close proximity to a SNP linked to breast density and increased breast cancer risk. The other SNPs related to the breast size were also found near the genes responsible for mammary development, estrogen regulation and breast cancer.

The results of the study provide an idea about the genetic basis behind normal breast development. The results also highlight the fact that some of the factors responsible for the breast development may also be responsible for breast cancer. Although the study does not prove that increased breast size leads to an increased risk of breast cancer, it throws light on the interactions between the breast structure and the risk of breast cancer.

Earlier Studies: An Association Between Breast Density And Breast Cancer

Cancer specialists tell us that the structure of the breast plays a complicated role in the development of breast cancer. The mammographic density of the breast, i.e. the percentage of non-fat breast tissue in a breast as measured during mammography, has been identified as one of the risk factors behind breast cancer. It is said that women with a high breast density are almost five times more likely to develop breast cancer compared to women with normal breast density. However, the reasons behind this association are not properly understood.

Similarly, body weight has also been associated with breast cancer risk. An increased weight at an early age is said to decrease both premenopausal and postmenopausal risk of developing breast cancer. But an increase in body weight during adulthood increases the risk of developing postmenopausal breast cancer.

Studies done in the past have also linkedbreast asymmetry to the risk of breast cancer. Generally, the left breast is larger than the right breast and the incidence of breast cancer is also higher in the left breast. Whether this is just a coincidence or some other factors play a role in this association is still not known.

A study conducted by the Department of Epidemiology, Harvard School of Public Health at Boston, Massachusetts has thrown another important association between handedness and breast cancer. In this study, data obtained from 7 centers involving 3918 cases of breast cancer and 11,712 subjects as controls was examined to find an association between handedness and laterality of breast cancer. The study found that a significant number of left handed women suffered from left sided breast cancer.

As another part of the same study, data obtained from 4 centers involving 2325 cases of breast cancer and 7008 controls was examined to find an association between the cup size and the risk of developing breast cancer. The results showed that in postmenopausal women, larger cup size was associated with an increased breast cancer risk.

A study published in the journal “Cancer Causes and Controls”, tried to establish the link between breast size and breast cancer risk and the laterality of the tumor. The study was carried out on 261 women with breast cancer and 291 controls. All the women were members of the United States' Breast Cancer Detection and Demonstration Project from 1973 to 1980. It was seen that the left breast was bigger in 53% of women with breast cancer and in 60% women from the control group. The data collected revealed that 51% of the women with breast cancer had left sided disease. It was also seen that cancerous growth was seen in the larger breast of 57% women with left sided diseases compared to 46% with right sided disease. In other words, breast size was predominantly linked to the risk of left sided breast cancer.

Another study has shown that in women with a BMI less than 25, those with a cup size of D or more were 1.8 times more likely to develop breast cancer compared to those with a cup size of A or less.

Although studies have brought out some degree of association between the breast size and the risk of breast cancer, according to Dr. Eriksson, the association is not very strong. Moreover, breast size is largely an inherited trait and it is more important to focus on the modifiable risk factors of breast cancer like obesity and alcohol use. It is these factors that a woman can change or influence so as to cut down on her risk of developing breast cancer.
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  • “Breast Cancer Risk Might Be Tied To Breast Size, Study Says”, by Catherine Pearson, published in the July 5, 2012 issue of the Huffington Post, accessed on August 10, 2012.
  • “Breast size, handedness and breast cancer risk”, by Hsieh CC, et al, published in the 1991 issue of the European Journal of Cancer, accessed on August 10, 2012.
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