Obesity and Breast Cancer: What’s The Link?
|
By Dr. James Aw, Medical Director The lifetime risk for being diagnosed with breast cancer for women is 1 in 9, according to the Canadian Cancer Society. Typical risk factors for breast cancer include:
Let’s take a look at hormone replacement therapy first, which has a higher risk for breast cancer when combined with estrogen-progestin replacement than compared to estrogen. In larger population based studies, there is a 1 to 2 per cent annual increased breast cancer risk with HRT, but this disappeared within 5 years of stopping treatment. More recently studies have found that breast cancer risk was higher if HRT began less than 5 years after the onset of menopause. Another risk factor is lifestyle. Certain lifestyle factors that have been identified include obesity, diet, lack of exercise, excessive daily alcohol intake, smoking and possibly vitamin D deficiency. Obesity is an established risk factor for post-menopausal breast cancer. The relationship between obesity and breast cancer is complex, but thought to be mainly associated with the increased production of estrogen in fatty tissues after menopause. An excess of circulating hormones can stimulate the growth of estrogen sensitive cancer cells. Obesity also effects other hormone levels (insulin, leptin, adiponectin via fat cells) and releases inflammatory mediators that promote tumour growth. In order to survive, cancer cells require an environment that promotes cancer cell growth and a cancer blood supply. Obesity leads to a complex metabolic pathway of increased or decreased production of various bio-chemicals and hormones that eventually affect the breast cancer cells’ ability to survive. Moreover, increasing evidence supports a strong association between type 2 diabetes and breast cancer. The biological explanation is that obesity affects insulin regulation. Undiagnosed or delayed diagnosed diabetes has been reported to occur in approximately 30 per cent of patients with breast cancer (US population data). Recently there has been a renewed interest in the use of the diabetic drug called metformin, for possible cancer prevention by inhibiting the growth of cancer cells. However - more research is required. A recent study by the Danish Breast Cancer Cooperative Group (over 50,000 patients followed over 30 years) found that obesity was an independent prognostic factor for the development and spread of cancer (metastases), and eventually death after the diagnosis of breast cancer. The risk for distant metastases was found to increase 46 per cent over the span of 10 years in obese women. Women with a higher BMI (>30) more often had breast cancers with poorer prognosis, larger tumour size and positive lymph nodes (i.e. spread of disease). Some studies have also suggested that cancer therapies may be less effective in overweight patients. The good news is healthy lifestyle choices can have an impact on decreasing your risk. Studies have shown that losing at least 10 per cent of body weight (in overweight individuals) can reduce the concentrations of hormones that affect cancer survival (i.e. estrogen, leptin, insulin). Weight loss can also increase anti-cancer hormones (i.e. sex hormone binding globulin, adiponectin) and reduce pro-inflammatory markers (i.e. cytokines). Newer drugs are being researched that might be able to target obesity related pathways by targeting specific hormones and receptors linked to cancer. Future screening may include standardized mammographic density guidelines and whole genome based research (since BRCA 1 and 2 gene mutations only account for approximately 5 per cent of breast cancers). How can Medcan help in the fight against breast cancer?
Most importantly, an overall healthy lifestyle should be reviewed with a nutritionist and fitness specialist to ensure a pro-active approach to avoid preventable obesity. The National Cancer Institute is an excellent reference for the latest research developments in Breast Cancer Prevention. |