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Obesity causes changes in breast tissue, promoting breast tumour growth

August 25th, 2015

Obesity is an important risk factor for many types of cancer. Studies have shown that obesity is associated with a moderate increase in breast cancer risk for post-menopausal women – but why?

It is thought an increased risk of breast cancer may be due to increased levels of oestrogen in obese post-menopausal women. After menopause, when the ovaries stop producing hormones, fat tissue becomes the most important source of oestrogen. Because obese women have more fat tissue, their oestrogen levels are higher, potentially leading to more rapid growth of oestrogen-responsive breast tumours.

Now, breast cancer researchers have gone one step further to examine the cellular, structural and molecular changes that happen in the breast tissue of obese animals and people.

The findings, published this week in Science Translational Medicine, found that obesity increases the stiffness of breast tissue. It is thought that the stiff breast tissue somehow interrupts the normal communication channels between cells, which in turn stimulates breast cancer growth.

The researchers found that precancerous cells (cells that have not yet become cancerous) in obese breast tissue were more likely to turn into breast cancer tumours than precancerous cells in lean breast tissue.

Interestingly, the changes that occur in obese breast tissue may be reversible. Researchers placed obese mice on a diet and studied their breast tissue as they lost weight. While weight loss reversed some of the tissue stiffness, it did not reverse all of the obesity-related tissue changes.

We know that overweight and obese women diagnosed with breast cancer tend to have poorer outcomes than women within a normal weight range. Despite this, there are few treatments specifically tailored for obese women.

These findings help to build our understanding of cellular changes that may increase the risk of breast cancer. They may also lead to a change in treatment strategies.

Currently, one practice of reconstructing the breast following mastectomy involves the use of fat tissue from the patient. It is possible that this practice will be reviewed, as the use of fat tissue may pose a risk of the tumour recurring.

It is also thought that the findings may be used to develop new drugs and treatment strategies better tailored to the individual body types of women with breast cancer.