Does Breast Size Influence Breast Cancer Risk?

The breast size of a woman keeps changing as she ages. At puberty, growth hormones and estrogen together cause breast development in girls. Breast size increases during pregnancy and breastfeeding. There is also a subtle increase in breast size during every menstrual cycle.

After menopause, the breasts go through atrophy. The term muscle atrophy refers to the loss of muscle tissue. Atrophy causes a reduction in breast size.

Breast Size And Breast Cancer Risk

Here are a few ways how breast size could contribute to breast cancer risk:

Difficulty In Identifying Tumors

Bigger breasts make it difficult to identify lumps. Most women meet with a doctor when they self-examine the breasts and find a possible lump. Women who have larger breasts may not be able to identify the tumor before it gets big enough to push through the fat layers.

Hence there can be a delay in diagnosis and treatment, increasing the risk of complications.

Big Breasts Are Associated With Obesity

Bigger breasts are commonly noticed in obese and overweight women. Obesity is a very significant non-genetic factor that increases breast cancer risk.

Bigger Breasts In Women With Normal BMI Levels

A study published in the International Journal of Cancer studied the relationship between breast size in premenopausal women and cancer risk.

The study assessed 89,268 premenopausal women in the age range of 29-47. They were followed up after 8 years. Out of these women, 803 had been diagnosed with breast cancer. The study recorded that women with BMI levels less than 25 and a bra cup size of more than D had a higher risk of developing breast cancer.

Breast Size & Breast Cancer Risk: The Genetic Angle

The ZNF703 Gene

The ZNF703 gene contains instructions for the production of Zinc Finger Protein 703. This gene has been associated with the development of breast cancer.

It behaves as a “classical oncogene” that regulates the growth and development of cells in breast cancer cell lines.

Oncogene is a mutated gene or gene containing errors that contribute to the development of cancer.

rs7816345

rs7816345 is a single nucleotide polymorphism or SNP in the ZNF703 gene. This SNP influences breast size and breast cancer risk.

The C allele of this SNP has been associated with bigger breast size and an increased risk for breast cancer.

Non-Genetic Factors

Geographical Location

According to some studies, breast cancer in women is less common in Asia than in Western countries. These studies report that this could be because the average breast size in Asian women is lesser than in Western countries, which brings down the risk.

Increased Levels of Adipose Tissue

Larger breasts have more adipose tissue. With more adipose tissue, the local estrogen levels increase. These local estrogen levels act as a slow-releasing source of carcinogens (cancer-causing agents). This increases the risk of developing breast cancer.

Breast Parenchymal Patterns

The breast parenchymal pattern is the proportion of glandular tissues to fatty tissues in the breasts. Glandular tissues in the breasts help make milk and include the lobes and ducts. A dense breast parenchyma pattern makes it difficult to identify tumors and hence causes diagnostic delays and complicates the cancer condition.

Hormone Replacement Therapy (HRT)

HRT is used in treating the symptoms of menopause. HRT helps in balancing the levels of estrogen and progesterone in the body.

According to a 2001 study, women who used HRT had increased breast density and hence had an increased risk of late diagnosis of breast cancer. Women who continued HRT for an extended period had consistently high breast densities throughout their life.

What You Could Do?

Genetic Testing

Genetic testing of BRCA genes can help you understand your risk for breast cancer. People with a family history of breast cancer or other risk factors should especially consider it.

Lose Weight

Obesity increases adipose tissues in the body, including in the breasts. This increases one’s risk of developing all kinds of cancer, including breast cancer. Losing weight can help bring down the risk considerably. Obese women with breast cancer have worse disease progression and lower overall survival rates.

Breast Augmentation Surgery

Breast augmentation surgery is a process of changing the shape, size, and look of breasts. Some women use silicone implants to improve the look of breasts. In the United States, 2 million women have opted for implants in the past.

A study analyzed the impact of breast implants in 11,676 women between the years 1973 and 1986. Out of these, only 41 patients ended up with breast cancer. The expected number in the usual population was around 86. This study hence reports that breast augmentation surgery brings down the risk of breast cancer.

Surgical Reduction Mammoplasty

This surgery is done to reduce the size of breasts. Here, breast tissues and excess skin from around the breasts are removed. Studies prove the number of breast cancer cases after surgical reduction mammoplasty was lesser than the expected numbers.

Summary

Breast size is one of the risk factors for breast cancer - bigger size is associated with a higher risk for breast cancer.
Increased difficulty in identifying lumps and increased estrogen production due to more adipose tissues in the breast can contribute to a higher risk of breast cancer.
Genes that influence your breast size can also influence your breast cancer risk.
Genetic testing of BRCA genes can help estimate breast cancer risk and be especially useful for women under the high-risk category.
Maintaining a healthy weight helps restore estrogen balance and reduce breast cancer risk.