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Type 2 Diabetes and Breast Cancer, What's the Risk?

Type 2 diabetes and breast cancer

If you are a postmenopausal women who has type 2 diabetes, a new study indicates your risk of breast cancer is significantly greater than women without diabetes. The question is, what's behind the increased risk of breast cancer in this specific population of women and can you do anything about it?

What is your risk of breast cancer?

Before looking at the long list of risk factors for breast cancer, the potential new addition deserves a closer look. That inspection is prompted by the work of investigators at the International Prevention Research Institute in France, who reviewed data from 40 studies of type 2 diabetes and breast cancer.

After evaluating data from more than 56,000 women with breast cancer, the researchers found that

  • Postmenopausal women with type 2 diabetes have a 27% increased risk of breast cancer than women without diabetes.
  • The increased risk of developing breast cancer was not seen in women who had type 1 diabetes or who had not gone through menopause

Investigators are uncertain why postmenopausal women with type 2 diabetes have an increased risk of breast cancer, although obesity is one possibility. Obesity is a risk factor for both type 2 diabetes and breast cancer.

In two previous studies, investigators found that older women who have type 2 diabetes may also be at increased risk of another types of cancer: colorectal cancer. One study conducted at the Mayo Clinic and another published in Cancer Causes & Control reported that women with diabetes had a significantly increased risk of colorectal cancer when compared with women without diabetes.

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Other risk factors for breast cancer
The list of risk factors for breast cancer is not short, and it can be separated into two categories: factors over which you have control, and those you do not. In addition to overweight and obesity, other risk factors for breast cancer over which people have control are:

  • Diet: It is widely held that consuming red meat, processed meats, and other sources of animal fat raise the risk of breast cancer.
  • Lack of exercise: There is evidence that exercise reduces breast cancer risk.
  • Smoking
  • Alcohol: Breast cancer risk increases with the amount of alcohol women consume.
  • Use of oral contraceptives: A higher risk of breast cancer is associated with recent use (within 10 years) of birth control pills.
  • Estrogen exposure: Factors that increase a woman's exposure to estrogen for prolonged periods of time without interruption can increase the risk, such as hormone use, overweight, and regular alcohol use.

Other risk factors for breast cancer cannot be controlled. They include

  • Being a woman: The most significant factor of all, primarily associated with the activity of estrogen and progesterone
  • Age: The risk increases significantly with age, rising from about a 1 in 233 risk at age 30 to 39 to a 1 in 27 risk by age 60
  • Family history: Having either a first-degree relative (e.g., mother, sister) or several blood relatives with breast or ovarian cancer places women at greater risk.
  • Race: White women have a slightly higher risk than do women of other ethnic groups
  • Radiation treatment. Women exposed to radiation of the chest as a child or young adult have a greater risk.
  • Prior breast cancer: Women who had breast cancer in the past are at higher risk of developing it again
  • Estrogen exposure: Females who begin menstruation before age 12, who go through menopause after 55, and/or who are exposed to estrogens from the environment have a prolonged exposure to estrogen
  • Pregnancy: Women who never experience a full-term pregnancy or who have their first full-term pregnancy after they are 30 have a greater risk.

What the new study means
The International Prevention Research Institute study did not identify the underlying reason for the increased risk of breast cancer among postmenopausal women with type 2 diabetes. Peter Boyle, the study's lead author and president of the Institute noted that the link could be direct or indirect.

That is, while overweight and obesity are a risk factor both type 2 diabetes and breast cancer share, the increased risk could be related to the impact of excess weight on hormone activity, which has an effect on biological mechanisms that prompt cancer growth.

Given the common risk factor, however, it makes sense for women who have type 2 diabetes to take steps to achieve and maintain a healthy weight to help reduce their risk of breast cancer and also improve their ability to control diabetes and ward off its associated complications.

Boyle P et al. Diabetes and breast cancer risk: a meta-analysis. British Journal of Cancer. 2012 Sept. 14
Flood A et al. Diabetes and risk of incident colorectal cancer in a prospective cohort of women. Cancer Causes Control 2010 Aug; 21(8): 1277-84

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