Is Breast Cancer Tied To Breast Size?

In a breakthrough study, researchers from a California based personal genomics company “23 and Me”, led by Dr. Nicholas Eriksson, found a possible link between a woman's breast size and the risk of developing breast cancer. Studies that were done earlier had already established an association between breast density and breast cancer. Studies have also shown a link between fat deposition on the body and breast cancer development. This study showed that the genes involved in breast size and those involved in development of breast cancer share some overlap for the first time, however.

 

The study, which was published in the journal BMC Medical Genetics, was conducted on 16,175 females of European ancestry. The investigators were trying to find out more about 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 the women's history of pregnancies or breast surgeries were taken into consideration when it came to publishing the final results.

 

 

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. The team was able to identify seven SNPs associated with a person's 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 breast development in women 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.

Cancer specialists have made it clear that the structure of the breast plays a complicated role in the development of breast cancer. The mammographic density of the breast, in other words the percentage of non-fat breast tissue in a breast as measured during a mammography, has been identified to be one of the risk factors behind breast cancer. It is said that women who have 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 at the current point.

 

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 linked breast asymmetry to an increased 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 that was conducted by the Department of Epidemiology, Harvard School of Public Health at Boston, Massachusetts has uncovered another interesting point — there is an important association between handedness (hand dominance) and breast cancer.

 

In this study, data that was gathered from 7 centers involving 3918 cases of breast cancer and 11,712 subjects without breast cancer as controls was examined. The aim was to discover whether there was an association between handedness and laterality of breast cancer. The study found that this was indeed the case, and that a significant number of left handed women suffered from left sided breast cancer.

As another part of the same study, which involved data obtained from 4 centers recording 2325 cases of breast cancer and 7008 controls who were not diagnosed with breast cancer was examined to find an association between a person's cup size and the risk of developing breast cancer. The results showed that in postmenopausal women, a larger cup size was associated with an increased risk of developing breast cancer.

A study published in the journal “Cancer Causes and Controls”, tried to establish a link between breast size and breast cancer risk and the laterality of the tumor. This particular study was smaller, looking at data from 261 women with breast cancer and 291 controls without breast cancer. All the women were members of the United States' Breast Cancer Detection and Demonstration Project from 1973 to 1980.

 

This research revealed 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 of 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. This means that a larger breast size is associated with a higher cancer risk in women with healthy weights.

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. Alongside those, participating in screening tests and doing regular breast self exams are important steps you can take.